13,000,000 Amylin Pharmaceuticals, Inc. Common Stock UNDERWRITING AGREEMENT

Exhibit 1.1

13,000,000

Amylin Pharmaceuticals, Inc.

Common Stock

UNDERWRITING AGREEMENT

March, 7, 2012

CREDIT SUISSE SECURITIES (USA) LLC,

Eleven Madison Avenue,

New York, N.Y. 10010-3629

Dear Sirs:

1. Introductory. Amylin Pharmaceuticals, Inc., a Delaware corporation (“Company”), agrees with Credit Suisse Securities (USA) LLC (“Credit Suisse”) to issue and sell 13,000,000 shares (“Firm Securities”) of its Common Stock, par value $0.001 per share, including related rights to purchase Series A Junior Participating Preferred Stock (“Securities”) and also proposes to issue and sell to Credit Suisse, at the option of Credit Suisse, an aggregate of not more than 1,950,000 additional shares (“Optional Securities”) of its Securities as set forth below. The Firm Securities and the Optional Securities are herein collectively called the “Offered Securities”.

2. Representations and Warranties of the Company. The Company represents and warrants to, and agrees with, Credit Suisse that:

(a) Filing and Effectiveness of Registration Statement; Certain Defined Terms. The Company has filed with the Commission a registration statement on Form S-3ASR (No. 333-179964), including a related prospectus or prospectuses, covering the registration of the Offered Securities under the Act, which has become effective. “Registration Statement” at any particular time means such registration statement in the form then filed with the Commission, including any amendment thereto, any document incorporated by reference therein and all 430B Information and all 430C Information with respect to such registration statement, that in any case has not been superseded or modified. “Registration Statement” without reference to a time means the Registration Statement as of the Effective Time. For purposes of this definition, 430B Information shall be considered to be included in the Registration Statement as of the time specified in Rule 430B.

For purposes of this Agreement:

“430B Information” means information included in a prospectus then deemed to be a part of the Registration Statement pursuant to Rule 430B(e) or retroactively deemed to be a part of the Registration Statement pursuant to Rule 430B(f).

“430C Information” means information included in a prospectus then deemed to be a part of the Registration Statement pursuant to Rule 430C.

“Act” means the Securities Act of 1933, as amended.

“Applicable Time” means 4:01 pm (Eastern time) on the date of this Agreement.

“Closing Date” has the meaning defined in Section 3 hereof.

“Commission” means the Securities and Exchange Commission.

“Effective Time” of the Registration Statement relating to the Offered Securities means the time of the first contract of sale for the Offered Securities.

“Exchange Act” means the Securities Exchange Act of 1934, as amended.

“Final Prospectus” means the Statutory Prospectus that discloses the public offering price, other 430B Information and other final terms of the Offered Securities and otherwise satisfies Section 10(a) of the Act.

“General Use Issuer Free Writing Prospectus” means any Issuer Free Writing Prospectus that is intended for general distribution to prospective investors, as evidenced by its being so specified in Schedule A to this Agreement.

“Issuer Free Writing Prospectus” means any “issuer free writing prospectus,” as defined in Rule 433, relating to the Offered Securities in the form filed or required to be filed with the Commission or, if not required to be filed, in the form retained in the Company’s records pursuant to Rule 433(g).

“Limited Use Issuer Free Writing Prospectus” means any Issuer Free Writing Prospectus that is not a General Use Issuer Free Writing Prospectus.

“Rules and Regulations” means the rules and regulations of the Commission.

“Securities Laws” means, collectively, the Sarbanes-Oxley Act of 2002 (“Sarbanes-Oxley”), the Act, the Exchange Act, the Rules and Regulations, the auditing principles, rules, standards and practices applicable to auditors of “issuers” (as defined in Sarbanes-Oxley) promulgated or approved by the Public Company Accounting Oversight Board and, as applicable, the rules of the New York Stock Exchange and the NASDAQ Stock Market (“Exchange Rules”).

“Statutory Prospectus” with reference to any particular time means the prospectus relating to the Offered Securities that is included in the Registration Statement immediately prior to that time, including any document incorporated by reference therein and all 430B Information and all 430C Information with respect to the Registration Statement. For purposes of the foregoing definition, 430B Information shall be considered to be included in the Statutory Prospectus only as of the actual time that form of prospectus (including a prospectus supplement) is filed with the Commission pursuant to Rule 424(b) and not retroactively.

Unless otherwise specified, a reference to a “rule” is to the indicated rule under the Act.

(b) Compliance with Securities Act Requirements. (i) (A) At the time the Registration Statement initially became effective, (B) at the time of each amendment thereto for the purposes of complying with Section 10(a)(3) of the Act (whether by post-effective amendment, incorporated report or form of prospectus), (C) at the Effective Time relating to the Offered Securities and (D) on the Closing Date, the Registration Statement conformed and will conform in all material respects to the requirements of the Act and the Rules and Regulations and did not and will not include any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary to make the statements therein, not misleading and (ii) (A) on its date, (B) at the time of filing the Final Prospectus pursuant to Rule 424(b) and (C) on the Closing Date, the Final Prospectus will conform in all material respects to the requirements of the Act and the Rules and Regulations, and will not include any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary to make the statements therein, in light of the circumstances under which they were made, not misleading. The preceding sentence does not apply to statements in or omissions from any such document based upon written information furnished to the Company by Credit Suisse specifically for use therein, it being understood and agreed that the only such information is that described as such in Section 8(b) hereof.

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(c) The documents incorporated by reference in the Registration Statement, the Final Prospectus and the General Disclosure Package, when they were filed with the Commission conformed in all respects to the requirements of the Act and the Rules and Regulations, and will not include any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary to make the statements therein not misleading and any further documents so filed and incorporated by reference in the Registration Statement, the Final Prospectus or the General Disclosure Package, when such documents are filed with the Commission, will conform in all respects to the requirements of the Act and the Rules and Regulations, and will not include any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary to make the statements therein not misleading.

(d) Automatic Shelf Registration Statement. (i) Well-Known Seasoned Issuer Status. (A) At the time of initial filing of the Registration Statement, (B) at the time of the most recent amendment thereto for the purposes of complying with Section 10(a)(3) of the Act (whether such amendment was by post-effective amendment, incorporated report filed pursuant to Section 13 or 15(d) of the Exchange Act or form of prospectus), and (C) at the time the Company or any person acting on its behalf (within the meaning, for this clause only, of Rule 163(c)) made any offer relating to the Offered Securities in reliance on the exemption of Rule 163, the Company was a “well known seasoned issuer” as defined in Rule 405, including not having been an “ineligible issuer” as defined in Rule 405.

(ii) Effectiveness of Automatic Shelf Registration Statement. The Registration Statement is an “automatic shelf registration statement,” as defined in Rule 405, that initially became effective within three years of the date of this Agreement. If immediately prior to the Renewal Deadline (as hereinafter defined), any of the Offered Securities remain unsold by Credit Suisse, the Company will prior to the Renewal Deadline file, if it has not already done so and is eligible to do so, a new automatic shelf registration statement relating to the Offered Securities, in a form satisfactory to Credit Suisse. If the Company is no longer eligible to file an automatic shelf registration statement, the Company will prior to the Renewal Deadline, if it has not already done so, file a new shelf registration statement relating to the Offered Securities, in a form satisfactory to Credit Suisse, and will use its best efforts to cause such registration statement to be declared effective within 180 days after the Renewal Deadline. The Company will take all other action necessary or appropriate to permit the public offering and sale of the Offered Securities to continue as contemplated in the expired registration statement relating to the Offered Securities. References herein to the Registration Statement shall include such new automatic shelf registration statement or such new shelf registration statement, as the case may be. “Renewal Deadline” means the third anniversary of the initial effective time of the Registration Statement.

(iii) Eligibility to Use Automatic Shelf Registration Form. The Company has not received from the Commission any notice pursuant to Rule 401(g)(2) objecting to use of the automatic shelf registration statement form. If at any time when Offered Securities remain unsold by Credit Suisse the Company receives from the Commission a notice pursuant to Rule 401(g)(2) or otherwise ceases to be eligible to use the automatic shelf registration statement form, the Company will (i) promptly notify Credit Suisse, (ii) promptly file a new registration statement or post-effective amendment on the proper form relating to the Offered Securities, in a form satisfactory to Credit Suisse, (iii) use its best efforts to cause such registration statement or post-effective amendment to be declared effective as soon as practicable, and (iv) promptly notify Credit Suisse of such effectiveness. The Company will take all other action necessary or appropriate to permit the public offering and sale of the Offered Securities to continue as contemplated in the registration statement that was the subject of the Rule 401(g)(2) notice or for which the

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Company has otherwise become ineligible. References herein to the Registration Statement shall include such new registration statement or post-effective amendment, as the case may be.

(iv) Filing Fees. The Company has paid or shall pay the required Commission filing fees relating to the Offered Securities within the time required by Rule 456(b)(1) without regard to the proviso therein and otherwise in accordance with Rules 456(b) and 457(r).

(e) Ineligible Issuer Status. (i) At the earliest time after the filing of the Registration Statement that the Company or another offering participant made a bona fide offer (within the meaning of Rule 164(h)(2)) of the Offered Securities and (ii) at the date of this Agreement, the Company was not and is not an “ineligible issuer,” as defined in Rule 405, including (x) the Company or any other subsidiary in the preceding three years not having been convicted of a felony or misdemeanor or having been made the subject of a judicial or administrative decree or order as described in Rule 405 and (y) the Company in the preceding three years not having been the subject of a bankruptcy petition or insolvency or similar proceeding, not having had a registration statement be the subject of a proceeding under Section 8 of the Act and not being the subject of a proceeding under Section 8A of the Act in connection with the offering of the Securities, all as described in Rule 405.

(f) General Disclosure Package. As of the Applicable Time, neither (i) the General Use Issuer Free Writing Prospectus(es) issued at or prior to the Applicable Time and, the preliminary prospectus supplement, dated March 7, 2012, including the base prospectus, dated March 7, 2012, (which is the most recent Statutory Prospectus distributed to investors generally), and the other information, if any, stated in Schedule A to this Agreement to be included in the General Disclosure Package, all considered together (collectively, the “General Disclosure Package”), nor (ii) any individual Limited Use Issuer Free Writing Prospectus, when considered together with the General Disclosure Package, included any untrue statement of a material fact or omitted to state any material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading. The preceding sentence does not apply to statements in or omissions from any Statutory Prospectus or any Issuer Free Writing Prospectus made in reliance upon and in conformity with written information furnished to the Company by Credit Suisse specifically for use therein, it being understood and agreed that the only such information furnished by Credit Suisse consists of the information described as such in Section 8(b) hereof.

(g) Issuer Free Writing Prospectuses. Each Issuer Free Writing Prospectus, as of its issue date and at all subsequent times through the completion of the public offer and sale of the Offered Securities or until any earlier date that the Company notified or notifies Credit Suisse as described in the next sentence, did not, does not and will not include any information that conflicted, conflicts or will conflict with the information then contained in the Registration Statement. If at any time following issuance of an Issuer Free Writing Prospectus there occurred or occurs an event or development as a result of which such Issuer Free Writing Prospectus conflicted or would conflict with the information then contained in the Registration Statement or as a result of which such Issuer Free Writing Prospectus, if republished immediately following such event or development, would include an untrue statement of a material fact or omitted or would omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading, (i) the Company has promptly notified or will promptly notify Credit Suisse and (ii) the Company has promptly amended or will promptly amend or supplement such Issuer Free Writing Prospectus to eliminate or correct such conflict, untrue statement or omission. The first sentence of this Section 2(g) does not apply to statements in or omissions from any Issuer Free Writing Prospectus made in reliance upon and in conformity with written information furnished to the Company by Credit Suisse specifically for

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use therein, it being understood and agreed that the only such information furnished by Credit Suisse consists of the information described as such in Section 8(b) hereof.

(h) Good standing of the Company. The Company has been duly incorporated and is existing as a corporation and in good standing under the laws of the State of Delaware, with power and authority (corporate and other) to own its properties and conduct its business as described in the General Disclosure Package; and the Company is duly qualified to do business as a foreign corporation in good standing in all other jurisdictions in which its ownership or lease of property or the conduct of its business requires such qualification, except where the failure to be so qualified or in good standing would not individually or in the aggregate have a material adverse effect on the condition (financial or otherwise), results of operations, business, properties, or prospects of the Company and its subsidiaries taken as a whole (“Material Adverse Effect”).

(i) Subsidiaries. Each subsidiary of the Company has been duly incorporated or organized, as the case may be, and is existing and in good standing under the laws of the jurisdiction of its incorporation or organization, with power and authority (corporate or other) to own its properties and conduct its business as described in the General Disclosure Package; and each subsidiary of the Company is duly qualified to do business as a foreign corporation or limited liability company in good standing in all other jurisdictions in which its ownership or lease of property or the conduct of its business requires such qualification, except where the failure to be so qualified or in good standing would not individually or in the aggregate have a Material Adverse Effect; all of the issued and outstanding capital stock or other ownership interests of each subsidiary of the Company has been duly authorized and validly issued and is fully paid and nonassessable; and the capital stock or other ownership interests of each subsidiary owned by the Company, directly or through subsidiaries, is owned free from liens, encumbrances and defects, except as disclosed in the General Disclosure Package. The subsidiaries of the Company listed on Schedule B hereto are the only subsidiaries, direct or indirect, of the Company and, except as disclosed in the General Disclosure Package, each subsidiary of the Company is a wholly-owned subsidiary, direct or indirect, of the Company.

(j) Offered Securities. The Offered Securities and all other outstanding shares of capital stock of the Company have been duly authorized; the authorized equity capitalization of the Company is as set forth in the General Disclosure Package; all outstanding shares of capital stock of the Company are, and, when the Offered Securities have been delivered and paid for in accordance with this Agreement on each Closing Date, such Offered Securities will have been, validly issued, fully paid and nonassessable, will conform in all material respects to the description thereof contained in the General Disclosure Package and to the description of such Offered Securities contained in the Final Prospectus; the stockholders of the Company have no preemptive rights with respect to the Securities; and none of the outstanding shares of capital stock of the Company have been issued in violation of any preemptive or similar rights of any security holder. Except as disclosed in the General Disclosure Package, there are no outstanding (A) securities or obligations of the Company convertible into or exchangeable for any capital stock of the Company, (B) warrants, rights or options to subscribe for or purchase from the Company any such capital stock or any such convertible or exchangeable securities or obligations or (C) obligations of the Company to issue or sell any shares of capital stock, any such convertible or exchangeable securities or obligations or any such warrants, rights or options. The Company has not, directly or indirectly, offered or sold any of the Offered Securities by means of any “prospectus” (within the meaning of the Act and the Rules and Regulations) or used any “prospectus” or made any offer (within the meaning of the Act and the Rules and Regulations) in connection with the offer or sale of the Offered Securities, in each case other than the Statutory Prospectus referred to in Section 2 hereof.

(k) Other Offerings. Except as disclosed in the General Disclosure Package, the Company has not sold, issued or distributed any common shares during the six-month period preceding the

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date hereof, including any sales pursuant to Rule 144A under, or Regulation D or S, of the Act, other than common shares issued pursuant to equity incentive, employee stock purchase, 401(k) and other plans, or pursuant to outstanding options, rights or warrants.

(l) No Finder’s Fee. Except as disclosed in the General Disclosure Package, there are no contracts, agreements or understandings between the Company and any person that would give rise to a valid claim against the Company or Credit Suisse for a brokerage commission, finder’s fee or other like payment in connection with this offering.

(m) Registration Rights. Except as disclosed in the General Disclosure Package, there are no contracts, agreements or understandings between the Company and any person granting such person the right to require the Company to file a registration statement under the Act with respect to any securities of the Company owned or to be owned by such person or to require the Company to include such securities in the securities registered pursuant to a Registration Statement or in any securities being registered pursuant to any other registration statement filed by the Company under the Act (collectively, “registration rights”), and any person to whom the Company has granted registration rights has agreed not to exercise such rights until after the expiration of the Lock-Up Period referred to in Section 5 hereof.

(n) Listing. If required, the Company has notified the NASDAQ Stock Market of the intended listing of the Offered Securities on the NASDAQ Global Select Market, subject to notice of issuance.

(o) Absence of Further Requirements. No consent, approval, authorization, or order of, or filing or registration with, any person (including any governmental agency or body or any court) is required to be obtained or made by the Company for the consummation of the transactions contemplated by this Agreement in connection with the offering, issuance and sale of the Offered Securities by the Company, except such as have been obtained, or made and such as may be required under state securities laws.

(p) Title to Property. Except as disclosed in the General Disclosure Package or as would not, individually or in the aggregate, reasonably be expected to have a Material Adverse Effect, the Company and its subsidiaries have good and marketable title to all real properties and all other properties and assets owned by them, in each case free from liens, charges, encumbrances and defects that would affect the value thereof or interfere with the use made or to be made thereof by them and, except as disclosed in the General Disclosure Package, the Company and its subsidiaries hold any leased real or personal property under valid and enforceable leases with no terms or provisions that would interfere with the use made or to be made thereof by them.

(q) Absence of Defaults and Conflicts Resulting from Transaction. The execution, delivery and performance of this Agreement, and the issuance and sale of the Offered Securities will not result in a breach or violation of any of the terms and provisions of, or constitute a default or a Debt Repayment Triggering Event (as defined below) under, or result in the imposition of any lien, charge or encumbrance upon any property or assets of the Company or any of its subsidiaries pursuant to, the charter or by-laws of the Company or any of its subsidiaries, any statute, rule, regulation or order of any governmental agency or body or any court, domestic or foreign, having jurisdiction over the Company or any of its subsidiaries or any of their properties, or any agreement or instrument to which the Company or any of its subsidiaries is a party or by which the Company or any of its subsidiaries is bound or to which any of the properties of the Company or any of its subsidiaries is subject; a “Debt Repayment Triggering Event” means any event or condition that gives, or with the giving of notice or lapse of time would give, the holder of any note, debenture, or other evidence of indebtedness (or any person acting on such holder’s behalf) the right to require the repurchase, redemption or repayment of all or a portion of such indebtedness by the Company or any of its subsidiaries.

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(r) Absence of Existing Defaults and Conflicts. Neither the Company nor any of its subsidiaries is in violation of its respective charter or by-laws or in default (or with the giving of notice or lapse of time would be in default) under any existing obligation, agreement, covenant or condition contained in any indenture, loan agreement, mortgage, lease or other agreement or instrument to which any of them is a party or by which any of them is bound or to which any of the properties of any of them is subject, except such defaults that would not, individually or in the aggregate, result in a Material Adverse Effect.

(s) No Material Adverse Change in Business. Except as disclosed in the General Disclosure Package, neither the Company nor any of its subsidiaries has sustained since the date of the latest audited financial statements included or incorporated by reference in the Statutory Prospectus any material loss or interference with its business from (i) fire, explosion, flood or other calamity, whether or not covered by insurance, or (ii) from any labor disturbance or dispute (iii) or any action, order or decree of any court or arbitrator or governmental or regulatory authority, and (iv) there has been no material transaction entered into and there is no material transaction that is probable of being entered into by the Company other than transactions in the ordinary course of business, and (v) there has been no obligation, direct or contingent, that is material to the Company taken as a whole, incurred by the Company, except as obligations incurred in the ordinary course of business in each case otherwise than as set forth or contemplated in the Statutory Prospectus; and, since the respective dates as of which information is given in the Registration Statement and the Statutory Prospectus, there has not been any change in the capital stock (excluding option and other securities grants in the ordinary course of business pursuant to the Company’s current equity incentive, employee stock purchase, 401(k) and other plans and the exercise of any outstanding stock options or warrants) or long-term debt of the Company or any of its subsidiaries (other than interest accruals) or any material adverse change, or any development involving a prospective material adverse change, in or affecting the general affairs, management, financial position, stockholders’ equity or results of operations of the Company and its subsidiaries, taken as a whole, otherwise than as set forth or contemplated in the Statutory Prospectus.

(t) Authorization of Agreement. This Agreement has been duly authorized, executed and delivered by the Company.

(u) Possession of Licenses and Permits. The Company and its subsidiaries possess, and are in compliance with the terms of, all certificates, authorizations, franchises, licenses and permits (“Licenses”) necessary to the conduct of the business now conducted and as described in the General Disclosure Package, except where failure to so possess or be in compliance with would not have a Material Adverse Effect, and have not received any notice of proceedings relating to the revocation or modification of any Licenses that, if determined adversely to the Company or any of its subsidiaries, would individually or in the aggregate, have a Material Adverse Effect.

(v) Absence of Labor Dispute. No labor dispute with the employees of the Company or any of its subsidiaries exists or, to the knowledge of the Company, is imminent that would have a Material Adverse Effect.

(w) Possession of Intellectual Property Rights. Except as disclosed in the Statutory Prospectus and Final Prospectus, the Company owns or has valid, binding and enforceable licenses or other rights to use any patents, trademarks, trade names, service marks, service names, copyrights, trade secrets, knowhow and other proprietary intellectual property rights (“Intellectual Property”) necessary to conduct the business of the Company in the manner in which it is being conducted; without having conducted any special searches or investigations over and above any searches that it may have conducted when deemed necessary or appropriate in connection with the filing of its patent applications, the Company believes that it will be able to conduct its business in the manner in which it is currently being conducted without any material conflict with the rights of

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others; the information contained in the Registration Statement, the Statutory Prospectus and the Final Prospectus concerning patents issued to, or patent applications filed on behalf of, the Company is accurate in all material respects; and, except as described in the Statutory Prospectus and Final Prospectus, the Company has not received any notice from any other person of infringement of or conflict with (and, without having conducted any special searches or investigations, knows of no such infringement of or conflict with) asserted rights of others with respect to any Intellectual Property or any trade secrets, proprietary information, inventions, knowhow, processes and procedures owned or used or licensed to the Company, which if determined adversely to the Company would, individually or in the aggregate, have a Material Adverse Effect.

(x) Environmental Laws. The Company and each of its subsidiaries is (i) in compliance with any and all applicable foreign, federal, state or local laws and regulations relating to the protection of human health and safety, the environment or hazardous or toxic substances or wastes, pollutants or contaminants (“Environmental Laws”), (ii) has received all permits, licenses or other approvals required of it under applicable Environmental Laws to conduct their respective business activities (“Environmental Permits”) and (iii) is in compliance with all terms and conditions of any such Environmental Permit, except where such noncompliance with Environmental Laws, failure to receive required Environmental Permits or failure to comply with the terms and conditions of such Environmental Permits would not, singly or in the aggregate, have a Material Adverse Effect. There are no costs or liabilities associated with Environmental Laws or Environmental Permits, including, without limitation, capital or operating expenditures required for cleanup, closure of properties or compliance with Environmental Laws or Environmental Permits, and any potential liability to third parties, of or relating to the Company or any of its subsidiaries, except for any costs or liabilities which would not, singly or in the aggregate, have a Material Adverse Effect or except as disclosed in the General Disclosure Package.

(y) Accurate Disclosure. The statements in the General Disclosure Package and the Final Prospectus under the headings “Material U.S. Federal Income and Estate Tax Consequences to Non-U.S. Holders” and “Description Of Capital Stock”, insofar as such statements summarize legal matters, agreements, documents or proceedings discussed therein, are in all material respects accurate and fair summaries of such legal matters, agreements, documents or proceedings.

(z) Absence of Manipulation. The Company has not taken, directly or indirectly, any action that is designed to or that has constituted or that would reasonably be expected to cause or result in the stabilization or manipulation of the price of any security of the Company to facilitate the sale or resale of the Offered Securities.

(aa) Statistical and Market-Related Data. Any third-party statistical and market-related data included or incorporated by reference in a Registration Statement, a Statutory Prospectus or the General Disclosure Package are based on or derived from sources that the Company believes to be reliable and accurate.

(bb) Internal Controls and Compliance with the Sarbanes-Oxley Act. Except as set forth in the General Disclosure Package, the Company, its subsidiaries and the Company’s Board of Directors (the “Board”) are in compliance in all material respects with Sarbanes-Oxley and all applicable Exchange Rules. The Company maintains a system of internal controls over accounting matters and financial reporting, and disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e))(collectively, “Internal Controls”) that comply with the Securities Laws and are sufficient to provide reasonable assurances that (i) transactions are executed in accordance with management’s general or specific authorizations, (ii) transactions are recorded as necessary to permit preparation of financial statements in conformity with U.S. General Accepted Accounting Principles and to maintain accountability for assets, (iii) access to assets is permitted only in accordance with management’s general or specific authorization and

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(iv) the recorded accountability for assets is compared with the existing assets at reasonable intervals and appropriate action is taken with respect to any differences. The Internal Controls are, or upon consummation of the offering of the Offered Securities will be, overseen by the Audit Committee (the “Audit Committee”) of the Board in accordance with Exchange Rules. The Company has not publicly disclosed or reported to the Audit Committee or the Board, and within the next 90 days the Company does not reasonably expect to publicly disclose or report to the Audit Committee or the Board, a significant deficiency, material weakness, change in Internal Controls or fraud involving management or other employees who have a significant role in Internal Controls (each, an “Internal Control Event”), any violation of, or failure to comply with, the Securities Laws, or any matter which, if determined adversely, would have a Material Adverse Effect.

(cc) Litigation. Except as disclosed in the General Disclosure Package, there are no pending actions, suits or proceedings (including any inquiries or investigations by any court or governmental agency or body, domestic or foreign) against or affecting the Company, any of its subsidiaries or any of their respective properties that, if determined adversely to the Company or any of its subsidiaries, would individually or in the aggregate have a Material Adverse Effect, or would materially and adversely affect the ability of the Company to perform its obligations under this Agreement, or which are otherwise material in the context of the sale of the Offered Securities; and no such actions, suits or proceedings (including any inquiries or investigations by any court or governmental agency or body, domestic or foreign) are, to the Company’s knowledge, threatened or contemplated.

(dd) Financial Statements. The financial statements included in the Registration Statement and the General Disclosure Package present fairly, in all material respects, the financial position of the Company and its consolidated subsidiaries as of the dates shown and their results of operations and cash flows for the periods shown, and, except as otherwise disclosed in the General Disclosure Package, such financial statements have been prepared in conformity with the generally accepted accounting principles in the United States applied on a consistent basis; and the schedules included in the Registration Statement present fairly, in all material respects, the information required to be stated therein.

(ee) Investment Company Act. The Company is not and, after giving effect to the offering and sale of the Offered Securities and the application of the proceeds thereof as described in the General Disclosure Package, will not be an “investment company” as defined in the Investment Company Act of 1940, as amended (the “Investment Company Act”).

(ff) No Unlawful Payments. Neither the Company nor any of its subsidiaries, nor any director, officer, nor to the Company’s knowledge, any agent, employee or other person associated with or acting on behalf of the Company or any of its subsidiaries, has (i) used any corporate funds for any unlawful contribution, gift, entertainment or other unlawful expense relating to political activity; (ii) made any direct or indirect unlawful payment to any foreign or domestic government official or employee from corporate funds; (iii) violated or in violation of any provision of the Foreign Corrupt Policies Act of 1977; or (iv) made any bribe, rebate, payoff, influence payment, kickback or other unlawful payment.

(gg) Compliance with Anti-Money Laundering Laws. The operations of the Company and its subsidiaries are and have been conducted at all times in compliance with applicable financial recordkeeping and reporting requirements of the Currency and Foreign Transactions Reporting Act of 1970, as amended, applicable anti-money laundering statutes of all jurisdictions, and the rules and regulations thereunder, and any related or similar applicable rules, regulations and guidelines issued, administered or enforced by any governmental agency (collectively, the “Anti-Money Laundering Laws”) and no action, suit or proceeding by or before any court or governmental agency, authority or body or any arbitrator involving the Company or any of its

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subsidiaries with respect to the Anti-Money Laundering Laws is pending or, to the knowledge of the Company, threatened.

(hh) Compliance with OFAC. None of the Company, any of its subsidiaries, any director, officer, or to the Company’s knowledge, any agent, employee or affiliate of the Company or any of its subsidiaries is currently subject to any U.S. sanctions administered by the Office of Foreign Assets Control of the U.S. Department of Treasury (“OFAC”); and the Company will not, directly or indirectly, use the proceeds of the offering and sale of the Offered Securities, or lend, contribute or otherwise make available such proceeds to any subsidiary, joint venture partner or other person or entity, for the purpose of financing the activities of any person currently subject to any U.S. sanctions administered by OFAC.

(ii) No Restrictions on Payments by Subsidiaries. No subsidiary of the Company is currently prohibited, directly or indirectly, under any agreement or other instrument to which it is a party or is subject, (i) from paying any dividends to the Company, (ii) from making any other distribution on such subsidiary’s capital stock, (iii) from repaying to the Company any loans or advances to such subsidiary from Company or (iv) from transferring any of such subsidiary’s material properties or assets to the Company or any other subsidiary of the Company.

(jj) Regulatory. The human clinical trials, animal studies and other preclinical tests conducted by the Company or its subsidiaries or in which the Company or its subsidiaries have participated or that are described in the General Disclosure Package or the results of which are referred to in the General Disclosure Package, and, to the Company’s knowledge, such studies and tests conducted on behalf of the Company or its subsidiaries, or that the Company or its subsidiaries currently intend to rely on in support of registrations by the United States Food and Drug Administration (the “FDA”) or foreign regulatory agencies for Byetta, Bydureon, Symlin, dual chamber cartridge pens combined with Bydureon, Metreleptin, AC165198, and use of neurohormones (collectively, the “Company Products”), were and, if still pending, are being conducted in material compliance with applicable laws. The descriptions of the results of such studies, tests and trials contained in the General Disclosure Package are accurate in all material respects, and, to the Company’s knowledge, there are no other trials, studies or tests, the results of which the Company believes reasonably call into question the clinical trial results described or referred to in the General Disclosure Package when viewed in the context in which such results are described and the clinical stage of development. Neither the Company nor any of its subsidiaries have received any notices or correspondence from the FDA or any other domestic or foreign governmental authority requiring the termination, suspension or material modification, other than modifications customarily implemented during the drug development process, of any preclinical tests or clinical trials conducted by or on behalf of the Company or its subsidiaries or in which the Company or its subsidiaries have participated that are described in the General Disclosure Package or the results of which are referred to in the General Disclosure Package, in each case that would have a Material Adverse Effect. Except as set forth in the General Disclosure Package, since January 1, 2010, the Company and its subsidiaries, and, to the Company’s knowledge, its distributors, manufacturers and sublicensees, are not subject to any obligation arising under an administrative or regulatory action, FDA inspection, FDA warning letter, FDA notice of violation letter, recall notice, or other notice or commitment made to or with the FDA or any other governmental authority (including without limitation the Drug Enforcement Agency) regarding or impacting the Company Products or any product candidate of the Company, including without limitation any notice alleging a material violation of any applicable law or required registration. Except as described in the General Disclosure Package, since January 1, 2010, neither the Company nor its subsidiaries and, to the Company’s knowledge, neither its distributors, manufacturers nor sublicensees, have received any written or other notice from the FDA, the Drug Enforcement Agency or a comparable governmental authority alleging that the Company Products are the subject of any pending or threatened investigation in any jurisdiction that has not been fully remedied. Except as described in the General Disclosure Package, the Company and its

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subsidiaries and, to the Company’s knowledge with respect to the Company Products, its distributors, manufacturers and sublicensees, are in compliance with all applicable laws administered or issued by the FDA or any other governmental authority, including, without limitation, those requirements relating to the testing, handling, distribution, regulatory approval, pricing approval, annual reporting, registration, good manufacturing practices, record-keeping, adverse event reporting, promotion, sales, packaging, labeling and advertising of drugs and controlled substances (where applicable) in each case in all material respects. The promotion, sale, manufacture, storage, packaging, labeling, handling, testing and distribution of the Company Products for which registrations have been obtained by the Company, its subsidiaries, distributors, manufacturers and sublicensees is being, and at all times following such registration has been, conducted in compliance in all material respects with the registrations, except for any failure that has not, and would not reasonably be expected to have, individually or in the aggregate, a Material Adverse Effect; provided that the foregoing representation as it relates to the Company’s distributors, manufacturers and sublicensees shall be to the Company’s knowledge. All regulatory filings made by the Company or its subsidiaries, or, to the Company’s knowledge, by the Company’s distributors, manufacturers or sublicensees, to any governmental authority, in each case with respect to any of the Company Products, when submitted to the governmental authority were accurate in all material respects as of the date of submission, or as subsequently corrected or modified. Neither the Company nor its subsidiaries (including their officers or employees) nor, to the Company’s knowledge, any principal investigator or sub-investigator engaged in any clinical investigation conducted with respect to any Company Product (including their officers or employees) has been convicted of any crime under 21 U.S.C. Section 335a(a) or any similar state or foreign law or under 21 U.S.C. Section 335a(b) or any similar state or foreign law. To the Company’s knowledge, there are no facts which would reasonably be expected to cause (i) the withdrawal or recall of any Company Product sold by or on behalf of the Company, its subsidiaries, distributors or sublicensees, (ii) a termination or suspension of marketing of any such Company Product, or (iii) any adverse events or safety concerns not already publicly disclosed that would have a material impact on the ability to market any such Company Product.

(kk) Accountants. Ernst & Young LLP, which has certified the financial statements of the Company included in, or incorporated by reference into, the General Disclosure Package and the Final Prospectus, is an independent registered public accounting firm with respect to the Company within the Rules and Regulations and as required by the Act and the applicable rules and guidance from the Public Company Accounting Oversight Board (United States). The summary and selected financial and statistical data included in the Registration Statement, the General Disclosure Package and the Final Prospectus presents fairly the information shown therein and such data has been compiled on a basis consistent with the financial statements presented therein and the books and records of the Company. The Company does not have any material liabilities or obligations, direct or contingent (including any off-balance sheet obligations or any “variable interest entities” within the meaning of Financial Accounting Standards Board Interpretation No. 46), not disclosed in the Registration Statement, the General Disclosure Package and the Final Prospectus. There are no financial statements that are required to be included in the Registration Statement, the General Disclosure Package or the Final Prospectus that are not included as required.

3. Purchase, Sale and Delivery of Offered Securities. On the basis of the representations, warranties and agreements and subject to the terms and conditions set forth herein, the Company agrees to sell to Credit Suisse, and Credit Suisse agrees to purchase from the Company, at a purchase price of $15.39 per share, 13,000,000 shares of Firm Securities.

The Company will deliver the Firm Securities to or as instructed by Credit Suisse in a form reasonably acceptable to Credit Suisse against payment of the purchase price by Credit Suisse in Federal (same day) funds by wire transfer to an account at a bank acceptable to Credit Suisse drawn to the order of the Company at the office of Davis Polk & Wardwell LLP, 1600 El Camino Real, Menlo Park, CA 94025,

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at 9:00 A.M., New York time, on March 13, 2012, or at such other time not later than seven full business days thereafter as Credit Suisse and the Company determine, such time being herein referred to as the “First Closing Date”. For purposes of Rule 15c6-1 under the Securities Exchange Act of 1934, the First Closing Date (if later than the otherwise applicable settlement date) shall be the settlement date for payment of funds and delivery of securities for all the Offered Securities sold pursuant to the offering. The Firm Securities so to be delivered or evidence of their issuance will be made available for checking at the above office of Davis Polk & Wardwell LLP at least 24 hours prior to the First Closing Date.

In addition, upon written notice from Credit Suisse given to the Company from time to time not more than 30 days subsequent to the date of the Final Prospectus, Credit Suisse may purchase all or less than all of the Optional Securities at the purchase price per Security to be paid for the Firm Securities. The Company agrees to sell to Credit Suisse the number of shares of Optional Securities specified in such notice and Credit Suisse agrees to purchase such Optional Securities. Such Optional Securities may be purchased by Credit Suisse only for the purpose of covering over-allotments made in connection with the sale of the Firm Securities. No Optional Securities shall be sold or delivered unless the Firm Securities previously have been, or simultaneously are, sold and delivered. The right to purchase the Optional Securities or any portion thereof may be exercised from time to time and to the extent not previously exercised may be surrendered and terminated at any time upon notice by Credit Suisse to the Company.

Each time for the delivery of and payment for the Optional Securities, being herein referred to as an “Optional Closing Date”, which may be the First Closing Date (the First Closing Date and each Optional Closing Date, if any, being sometimes referred to as a “Closing Date”), shall be determined by Credit Suisse but shall be not earlier than two full business days nor later than five full business days after such written notice of election to purchase Optional Securities is given; provided however that if the notice of election to purchase Optional Securities is delivered to the Company prior to the First Closing Date, the applicable Closing Date may take as early as one full business day after such delivery; provided further however that if the First Closing Date and the Optional Closing Date are simultaneous, notice shall be provided prior to the Closing Date. The Company will deliver the Optional Securities being purchased on each Optional Closing Date to or as instructed by Credit Suisse in a form reasonably acceptable to Credit Suisse against payment of the purchase price therefor in Federal (same day) funds by wire transfer to an account at a bank acceptable to Credit Suisse drawn to the order of the Company, at the above office of Davis Polk & Wardwell LLP. The Optional Securities being purchased on each Optional Closing Date or evidence of their issuance will be made available for checking at the above office of Davis Polk & Wardwell LLP at a reasonable time in advance of such Optional Closing Date.

4. Offering by Credit Suisse. It is understood that Credit Suisse proposes to offer the Offered Securities for sale to the public as set forth in the Final Prospectus.

5. Certain Agreements of the Company. The Company agrees with Credit Suisse that:

(a) Filing of Prospectuses. The Company has filed or will file each Statutory Prospectus (including the Final Prospectus) pursuant to and in accordance with Rule 424(b)(2) (or, if applicable and consented to by Credit Suisse, subparagraph (5)) not later than the second business day following the earlier of the date it is first used or the execution and delivery of this Agreement. The Company has complied and will comply with Rule 433.

(b) Filing of Amendments; Response to Commission Requests. The Company will promptly advise Credit Suisse of any proposal to amend or supplement the Registration Statement or any Statutory Prospectus at any time and will offer Credit Suisse a reasonable opportunity to comment on any such amendment or supplement; and the Company will also advise Credit Suisse promptly of (i) the filing of any such amendment or supplement, (ii) any request by the Commission or its staff for any amendment to the Registration Statement, for any supplement to any Statutory Prospectus or for any additional information, (iii) the institution by the Commission of any stop order proceedings in respect of the Registration Statement or the threatening of any proceeding for

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that purpose, and (iv) the receipt by the Company of any notification with respect to the suspension of the qualification of the Offered Securities in any jurisdiction or the institution or threatening of any proceedings for such purpose. The Company will use its reasonable best efforts to prevent the issuance of any such stop order or the suspension of any such qualification and, if issued, to obtain as soon as possible the withdrawal thereof.

(c) Continued Compliance with Securities Laws. If, at any time when a prospectus relating to the Offered Securities is (or but for the exemption in Rule 172 would be) required to be delivered under the Act by any underwriter or dealer, any event occurs as a result of which the Final Prospectus as then amended or supplemented would include an untrue statement of a material fact or omit to state any material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading, or if it is necessary at any time to amend the Registration Statement or supplement the Final Prospectus to comply with the Act, the Company will promptly notify Credit Suisse of such event and will as promptly as practical prepare and file with the Commission and furnish, at its own expense, to Credit Suisse and the dealers and any other dealers upon reasonable request of Credit Suisse, an amendment or supplement which will correct such statement or omission or an amendment which will effect such compliance. Neither Credit Suisse’s consent to, nor Credit Suisse’s delivery of, any such amendment or supplement shall constitute a waiver of any of the conditions set forth in Section 7 hereof.

(d) Rule 158. As soon as practicable, but not later than 16 months, after the date of this Agreement, the Company will make generally available to its securityholders an earnings statement (which need not be audited) covering a period of at least 12 months beginning after the date of this Agreement and satisfying the provisions of Section 11(a) of the Act and Rule 158.

(e) Furnishing of Prospectuses. The Company will furnish to Credit Suisse copies of the Registration Statement, including all exhibits, any Statutory Prospectus, the Final Prospectus and all amendments and supplements to such documents, in each case as soon as available and in such quantities as Credit Suisse reasonably requests. The Company will pay the expenses of printing and distributing to Credit Suisse all such documents.

(f) Blue Sky Qualifications. The Company will cooperate with Credit Suisse and its counsel to qualify the Offered Securities for sale under the applicable securities laws of such jurisdictions as Credit Suisse may reasonably designate and will continue such qualifications in effect so long as required for the distribution of the Offered Securities as contemplated hereby; provided that, in connection therewith, the Company will not be required to file a general consent to service of process or to qualify as a foreign corporation or as a dealer in securities in any jurisdiction in which it is not so qualified, or subject itself to taxation for doing business in any jurisdiction in which it is not otherwise so subject.

(g) Reporting Requirements. During the period of three years hereafter, the Company will furnish to Credit Suisse as soon as practicable after the end of each fiscal year, a copy of its annual report to stockholders for such year; and the Company will furnish to Credit Suisse (i) as soon as available, a copy of each report and any definitive proxy statement of the Company filed with the Commission under the Exchange Act or mailed to stockholders, and (ii) from time to time, such other information concerning the Company as Credit Suisse may reasonably request, as permitted by applicable law; provided that if Credit Suisse shall request nonpublic confidential information the Company shall only be required to provide Credit Suisse with such information if Credit Suisse shall enter into a customary confidentiality agreement with the Company with respect thereto. However, so long as the Company is subject to the reporting requirements of either Section 13 or Section 15(d) of the Exchange Act and is timely filing reports with the Commission on its Electronic Data Gathering, Analysis and Retrieval system (“EDGAR”), or the information

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is available on the Company’s website, it is not required to furnish such reports or statements to Credit Suisse.

(h) Payment of Expenses. The Company will pay all expenses incident to the performance of its obligations under this Agreement, including but not limited to (i) any filing fees and other expenses (including reasonable fees and disbursements of counsel to Credit Suisse) incurred in connection with qualification of the Offered Securities for sale under the laws of such jurisdictions as Credit Suisse reasonably designates and the preparation and printing of memoranda relating thereto, (ii) costs and expenses related to the review by the Financial Industry Regulatory Authority of the Offered Securities (including filing fees and the reasonable fees and expenses of counsel for Credit Suisse relating to such review), (iii) costs and expenses relating to investor presentations or any “road show” in connection with the offering and sale of the Offered Securities including, without limitation, any travel expenses of the Company’s officers and employees and any other expenses of the Company including the chartering of airplanes, (iv) fees and expenses incident to listing the Offered Securities on the New York Stock Exchange, American Stock Exchange, NASDAQ Stock Market and other national and foreign exchanges, (v) fees and expenses in connection with the registration of the Offered Securities under the Exchange Act, and (vi) expenses incurred in distributing preliminary prospectuses and the Final Prospectus (including any amendments and supplements thereto) to Credit Suisse and for expenses incurred for preparing, printing and distributing any Issuer Free Writing Prospectuses to investors or prospective investors.

(i) Use of Proceeds. The Company will use the net proceeds received in connection with this offering in the manner described in the “Use of Proceeds” section of the General Disclosure Package and, except as disclosed in the General Disclosure Package, the Company does not intend to use any of the proceeds from the sale of the Offered Securities hereunder to repay any outstanding debt owed to any affiliate of Credit Suisse.

(j) Absence of Manipulation. The Company will not take, directly or indirectly, any action designed to or that would constitute or that might reasonably be expected to cause or result in, stabilization or manipulation of the price of any securities of the Company to facilitate the sale or resale of the Offered Securities; provided however, that no representation is made with regard to any actions of Credit Suisse.

(k) Restriction on Sale of Securities. For the period specified below (the “Lock-Up Period”), the Company will not, directly or indirectly, take any of the following actions with respect to its Securities or any securities convertible into or exchangeable or exercisable for any of its Securities (“Lock-Up Securities”): (i) offer, sell, issue, contract to sell, pledge or otherwise dispose of Lock-Up Securities, (ii) offer, sell, issue, contract to sell, contract to purchase or grant any option, right or warrant to purchase Lock-Up Securities, (iii) enter into any swap, hedge or any other agreement that transfers, in whole or in part, the economic consequences of ownership of Lock-Up Securities, (iv) establish or increase a put equivalent position or liquidate or decrease a call equivalent position in Lock-Up Securities within the meaning of Section 16 of the Exchange Act or (v) file with the Commission a registration statement under the Act relating to Lock-Up Securities, or publicly disclose the intention to take any such action, without the prior written consent of Credit Suisse, except (A) issuances of Lock-Up Securities pursuant to the conversion or exchange of convertible or exchangeable securities or the exercise of warrants or options, in each case outstanding on the date hereof or issuable as permitted in clause (B) below, and described in the General Disclosure Package, and (B) grants of stock options and other securities pursuant to the terms of a plan in effect on the date hereof and described in the General Disclosure Package, and (C) issuances of Lock-Up Securities to one or more counterparties in connection with the consummation of a strategic partnership, joint venture, collaboration, merger or the acquisition or license of any business products or technology; provided that, with respect to this clause (C), (1) the sum of the aggregate number of Lock-Up Securities so issued shall not exceed 5% of the

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total outstanding Securities immediately following the completion of this offering of Offered Securities and (2) prior to the issuance of such Lock-Up Securities each recipient of such Lock-Up Securities agrees in writing not to sell, offer, dispose of or otherwise transfer any such Lock-Up Securities during the Lock-Up Period without the prior written consent of Credit Suisse. The initial Lock-Up Period will commence on the date hereof and continue for 60 days after the date hereof or such earlier date that Credit Suisse consents to in writing.

6. Free Writing Prospectuses. The Company represents and agrees that, unless it obtains the prior consent of Credit Suisse, and Credit Suisse represents and agrees that, unless it obtains the prior consent of the Company, it has not made and will not make any offer relating to the Offered Securities that would constitute an Issuer Free Writing Prospectus, or that would otherwise constitute a “free writing prospectus,” as defined in Rule 405, required to be filed with the Commission. Any such free writing prospectus consented to by the Company and Credit Suisse is hereinafter referred to as a “Permitted Free Writing Prospectus.” The Company represents that it has treated and agrees that it will treat each Permitted Free Writing Prospectus as an “issuer free writing prospectus,” as defined in Rule 433, and has complied and will comply with the requirements of Rules 164 and 433 applicable to any Permitted Free Writing Prospectus, including timely Commission filing where required, legending and record keeping.

7. Conditions of the Obligations of Credit Suisse. The obligations of Credit Suisse to purchase and pay for the Firm Securities on the First Closing Date and the Optional Securities to be purchased on each Optional Closing Date will be subject to the accuracy of the representations and warranties of the Company herein (as though made on such Closing Date), to the accuracy of the statements of Company officers made pursuant to the provisions hereof, to the performance by the Company of its obligations hereunder and to the following additional conditions precedent:

(a) Accountants’ Comfort Letter. Credit Suisse shall have received letters, dated, respectively, the date hereof and each Closing Date, of Ernst & Young LLP, confirming that they are a registered public accounting firm and independent public accountants within the meaning of the Securities Laws and in the form of Schedule C hereto (except that, in any letter dated a Closing Date, the specified date referred to in Schedule C hereto shall be a date no more than three business days prior to such Closing Date).

(b) Filing of Prospectus. The Final Prospectus shall have been filed with the Commission in accordance with the Rules and Regulations and Section 5(a) hereof. Prior to such Closing Date, no stop order suspending the effectiveness of the Registration Statement or of any part thereof shall have been issued and no proceedings for that purpose shall have been instituted or, to the knowledge of the Company or Credit Suisse, shall be contemplated by the Commission.

(c) No Material Adverse Change. Subsequent to the execution and delivery of this Agreement, there shall not have occurred (i) any change, or any development or event involving a prospective change, in the condition (financial or otherwise), results of operations, business, properties, or prospects of the Company and its subsidiaries taken as a whole which, in the judgment of Credit Suisse, is material and adverse and makes it impractical or inadvisable to market the Offered Securities; (ii) any downgrading in the rating of any debt securities or preferred stock of the Company by any “nationally recognized statistical rating organization” (as defined for purposes of Section 3(a)(62) of the Exchange Act), or any public announcement that any such organization has under surveillance or review its rating of any debt securities or preferred stock of the Company (other than an announcement with positive implications of a possible upgrading, and no implication of a possible downgrading, of such rating) or any announcement that the Company has been placed on negative outlook; (iii) any change in U.S. or international financial, political or economic conditions or currency exchange rates or exchange controls the effect of which is such as to make it, in the judgment of Credit Suisse, impractical to market or to enforce contracts for the sale of the Offered Securities, whether in the primary market or in respect of dealings in the secondary market; (iv) any suspension or material limitation of trading in

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securities generally on the New York Stock Exchange or the NASDAQ Global Select Market, or any setting of minimum or maximum prices for trading on such exchanges; (v) or any suspension of trading of any securities of the Company on any exchange or in the over-the-counter market; (vi) any banking moratorium declared by any U.S. federal or New York authorities; (vii) any major disruption of settlements of securities, payment, or clearance services in the United States or any other country where such securities are listed or (viii) any attack on, outbreak or escalation of hostilities or act of terrorism involving the United States, any declaration of war by Congress or any other national or international calamity or emergency if, in the judgment of Credit Suisse, the effect of any such attack, outbreak, escalation, act, declaration, calamity or emergency is such as to make it impractical or inadvisable to market the Offered Securities or to enforce contracts for the sale of the Offered Securities.

(d) Lock-Up Letters. Credit Suisse shall have received lock-up letters, each substantially in the form of Exhibit A hereto, from each of its directors and “officers” (within the meaning of Rule 16a-1(f) under the Exchange Act), delivered to Credit Suisse on or before the date hereof, which lock-up letters shall be in full force and effect on the Closing Date.

(e) Opinion of Counsel for Company. Credit Suisse shall have received an opinion and negative assurance letter, dated such Closing Date, of Cooley LLP, counsel for the Company, in the forms set forth in Exhibits B-1 and B-2 hereto.

(f) Opinion of Counsel for Credit Suisse. Credit Suisse shall have received from Davis Polk & Wardwell LLP, counsel for Credit Suisse, such opinion or opinions, dated such Closing Date, with respect to such matters as Credit Suisse may require, and the Company shall have furnished to such counsel such documents as they reasonably request for the purpose of enabling them to pass upon such matters.

(g) Officer’s Certificate. Credit Suisse shall have received a certificate, dated such Closing Date, of an executive officer of the Company and a principal financial or accounting officer of the Company in which such officers shall state that: the representations and warranties of the Company in this Agreement are true and correct; the Company has complied with all agreements and satisfied all conditions on its part to be performed or satisfied hereunder at or prior to such Closing Date; no stop order suspending the effectiveness of the Registration Statement has been issued and no proceedings for that purpose have been instituted or, to their knowledge, are contemplated by the Commission; and, subsequent to the date of the most recent financial statements in the General Disclosure Package, there has been no material adverse change, nor any development or event involving a prospective material adverse change, in the condition (financial or otherwise), results of operations, business properties, or prospects of the Company and its subsidiaries taken as a whole except as set forth in the General Disclosure Package or as described in such certificate.

The Company will furnish Credit Suisse with such conformed copies of such opinions, certificates, letters and documents as Credit Suisse reasonably requests. Credit Suisse may waive compliance with any conditions to its obligations hereunder, whether in respect of an Optional Closing Date or otherwise.

8. Indemnification and Contribution. (a) Indemnification of Credit Suisse. The Company will indemnify and hold harmless Credit Suisse, its partners, members, directors, officers, employees, agents, affiliates and each person, if any, who controls Credit Suisse within the meaning of Section 15 of the Act or Section 20 of the Exchange Act (each, an “Indemnified Party”), against any and all losses, claims, damages or liabilities, joint or several, to which such Indemnified Party may become subject, under the Act, the Exchange Act, other Federal or state statutory law or regulation or otherwise, insofar as such losses, claims, damages or liabilities (or actions in respect thereof) arise out of or are based upon any untrue statement or alleged untrue statement of any material fact contained in any part of the Registration Statement at any time, any Statutory Prospectus as of any time, the Final Prospectus or any Issuer Free

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Writing Prospectus, or arise out of or are based upon the omission or alleged omission of a material fact required to be stated therein or necessary to make the statements therein not misleading, and will reimburse each Indemnified Party for any legal or other expenses reasonably incurred by such Indemnified Party in connection with investigating or defending against any loss, claim, damage, liability, action, litigation, investigation or proceeding whatsoever (whether or not such Indemnified Party is a party thereto), whether threatened or commenced, and in connection with the enforcement of this provision with respect to any of the above as such expenses are incurred; provided, however, that the Company will not be liable in any such case to the extent that any such loss, claim, damage or liability arises out of or is based upon an untrue statement or alleged untrue statement in or omission or alleged omission from any of such documents in reliance upon and in conformity with written information furnished to the Company by Credit Suisse specifically for use therein, it being understood and agreed that the only such information furnished by Credit Suisse consists of the information described as such in subsection (b) below.

(b) Indemnification of Company. Credit Suisse will indemnify and hold harmless the Company, each of its directors and each of its officers who signs a Registration Statement and each person, if any, who controls the Company within the meaning of Section 15 of the Act or Section 20 of the Exchange Act (each, a “Credit Suisse Indemnified Party”), against any losses, claims, damages or liabilities to which such Credit Suisse Indemnified Party may become subject, under the Act, the Exchange Act, other Federal or state statutory law or regulation or otherwise, insofar as such losses, claims, damages or liabilities (or actions in respect thereof) arise out of or are based upon any untrue statement or alleged untrue statement of any material fact contained in any part of the Registration Statement at any time, any Statutory Prospectus as of any time, the Final Prospectus, or any Issuer Free Writing Prospectus, or arise out of or are based upon the omission or the alleged omission of a material fact required to be stated therein or necessary to make the statements therein not misleading, in each case to the extent, but only to the extent, that such untrue statement or alleged untrue statement or omission or alleged omission was made in reliance upon and in conformity with written information furnished to the Company by Credit Suisse specifically for use therein, and will reimburse any legal or other expenses reasonably incurred by such Credit Suisse Indemnified Party in connection with investigating or defending against any such loss, claim, damage, liability, action, litigation, investigation or proceeding whatsoever (whether or not such Credit Suisse Indemnified Party is a party thereto), whether threatened or commenced, based upon any such untrue statement or omission, or any such alleged untrue statement or omission as such expenses are incurred, it being understood and agreed that the only such information furnished by Credit Suisse consists of (i) the following information in the Final Prospectus furnished on behalf of Credit Suisse: the concession figure appearing in the 4th paragraph under the caption “Underwriting” and the information contained in the 10th paragraph under the caption “Underwriting”.

(c) Actions Against Parties; Notification. Promptly after receipt by an indemnified party under this Section of notice of the commencement of any action, such indemnified party will, if a claim in respect thereof is to be made against the indemnifying party under subsection (a) or (b) above, notify the indemnifying party of the commencement thereof; but the failure to notify the indemnifying party shall not relieve it from any liability that it may have under subsection (a) or (b) above except to the extent that it has been materially prejudiced (through the forfeiture of substantive rights or defenses) by such failure; and provided further that the failure to notify the indemnifying party shall not relieve it from any liability that it may have to an indemnified party otherwise than under subsection (a) or (b) above. In case any such action is brought against any indemnified party and it notifies the indemnifying party of the commencement thereof, the indemnifying party will be entitled to participate therein and, to the extent that it may wish, jointly with any other indemnifying party similarly notified, to assume the defense thereof, with counsel satisfactory to such indemnified party (who shall not, except with the consent of the indemnified party, be counsel to the indemnifying party), and after notice from the indemnifying party to such indemnified party of its election so to assume the defense thereof, the indemnifying party will not be liable to such indemnified party under this Section for any legal or other expenses subsequently incurred by such indemnified party in connection with the defense thereof other than reasonable costs of investigation. No indemnifying party shall, without the prior written consent of the indemnified party, effect any settlement of any pending or threatened action in respect of which any indemnified party is or could have been a party

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and indemnity could have been sought hereunder by such indemnified party unless such settlement (i) includes an unconditional release of such indemnified party from all liability on any claims that are the subject matter of such action and (ii) does not include a statement as to, or an admission of, fault, culpability or a failure to act by or on behalf of an indemnified party.

(d) Contribution. If the indemnification provided for in this Section is unavailable or insufficient to hold harmless an indemnified party under subsection (a) or (b) above, then each indemnifying party shall contribute to the amount paid or payable by such indemnified party as a result of the losses, claims, damages or liabilities referred to in subsection (a) or (b) above (i) in such proportion as is appropriate to reflect the relative benefits received by the Company on the one hand and Credit Suisse on the other from the offering of the Offered Securities or (ii) if the allocation provided by clause (i) above is not permitted by applicable law, in such proportion as is appropriate to reflect not only the relative benefits referred to in clause (i) above but also the relative fault of the Company on the one hand and Credit Suisse on the other in connection with the statements or omissions which resulted in such losses, claims, damages or liabilities as well as any other relevant equitable considerations. The relative benefits received by the Company on the one hand and Credit Suisse on the other shall be deemed to be in the same proportion as the total net proceeds from the offering (before deducting expenses) received by the Company bear to the total underwriting discounts and commissions received by Credit Suisse. The relative fault shall be determined by reference to, among other things, whether the untrue or alleged untrue statement of a material fact or the omission or alleged omission to state a material fact relates to information supplied by the Company or Credit Suisse and the parties’ relative intent, knowledge, access to information and opportunity to correct or prevent such untrue statement or omission. The amount paid by an indemnified party as a result of the losses, claims, damages or liabilities referred to in the first sentence of this subsection (d) shall be deemed to include any legal or other expenses reasonably incurred by such indemnified party in connection with investigating or defending any action or claim which is the subject of this subsection (d). Notwithstanding the provisions of this subsection (d), Credit Suisse shall not be required to contribute any amount in excess of the amount by which the total price at which the Securities underwritten by it and distributed to the public were offered to the public exceeds the amount of any damages which Credit Suisse has otherwise been required to pay by reason of such untrue or alleged untrue statement or omission or alleged omission. No person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Act) shall be entitled to contribution from any person who was not guilty of such fraudulent misrepresentation. The Company and Credit Suisse agree that it would not be just and equitable if contribution pursuant to this Section 8(d) were determined by pro rata allocation or by any other method of allocation which does not take account of the equitable considerations referred to in this Section 8(d).

9. Default of Credit Suisse. If Credit Suisse defaults in its obligations to purchase Offered Securities hereunder on either the First or any Optional Closing Date and arrangements satisfactory to Credit Suisse and the Company for the purchase of such Offered Securities by other persons are not made within 36 hours after such default, this Agreement will terminate without liability on the part of the Company, except as provided in Section 10 (provided that if such default occurs with respect to Optional Securities after the First Closing Date, this Agreement will not terminate as to the Firm Securities or any Optional Securities purchased prior to such termination). Nothing herein will relieve Credit Suisse from liability for its default.

10. Survival of Certain Representations and Obligations. The respective indemnities, agreements, representations, warranties and other statements of the Company and of Credit Suisse set forth in or made pursuant to this Agreement will remain in full force and effect, regardless of any investigation, or statement as to the results thereof, made by or on behalf of Credit Suisse, the Company or any of their respective representatives, officers or directors or any controlling person, and will survive delivery of and payment for the Offered Securities. If the purchase of the Offered Securities by Credit Suisse is not consummated for any reason other than solely because of the termination of this Agreement pursuant to Section 9 hereof, the Company will reimburse Credit Suisse for all out-of-pocket expenses (including fees and disbursements of counsel) reasonably incurred by them in connection with the offering of the Offered Securities, and the respective obligations of the Company and Credit Suisse pursuant to Section 8 hereof

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shall remain in effect; provided however that, if such failure to consummate shall take place after the First Closing Date with respect to any Optional Securities, such reimbursement will be limited to the reasonable out-of-pocket expenses incurred after the First Closing Date solely with respect to such Optional Securities. In addition, if any Offered Securities have been purchased hereunder, the representations and warranties in Section 2 and all obligations under Section 5 shall also remain in effect.

11. Notices. All communications hereunder will be in writing and, if sent to Credit Suisse, will be mailed, delivered or telegraphed and confirmed to Credit Suisse at Eleven Madison Avenue, New York, N.Y. 10010-3629, Attention: LCD-IBD, or, if sent to the Company, will be mailed, delivered or telegraphed and confirmed to it at 9360 Towne Centre Drive, San Diego, California, 92121, Attention: Harry Leonhardt, Esq.

12. Successors. This Agreement will inure to the benefit of and be binding upon the parties hereto and their respective successors and the officers and directors and controlling persons referred to in Section 8, and no other person will have any right or obligation hereunder.

13. Counterparts. This Agreement may be executed in any number of counterparts, each of which shall be deemed to be an original, but all such counterparts shall together constitute one and the same Agreement.

14. Absence of Fiduciary Relationship. The Company acknowledges and agrees that:

(a) No Other Relationship. Credit Suisse has been retained solely to act as underwriter in connection with the sale of Offered Securities and that no fiduciary, advisory or agency relationship between the Company and Credit Suisse has been created in respect of any of the transactions contemplated by this Agreement or the Final Prospectus, irrespective of whether Credit Suisse has advised or is advising the Company on other matters;

(b) Arms’ Length Negotiations. The price of the Offered Securities set forth in this Agreement was established by the Company following discussions and arms-length negotiations with Credit Suisse and the Company is capable of evaluating and understanding and understands and accepts the terms, risks and conditions of the transactions contemplated by this Agreement;

(c) Absence of Obligation to Disclose. The Company has been advised that Credit Suisse and its affiliates are engaged in a broad range of transactions which may involve interests that differ from those of the Company and that Credit Suisse has no obligation to disclose such interests and transactions to the Company by virtue of any fiduciary, advisory or agency relationship; and

(d) Waiver. The Company waives, to the fullest extent permitted by law, any claims it may have against Credit Suisse for breach of fiduciary duty or alleged breach of fiduciary duty in connection with the transactions contemplated hereby and with the process leading to such transactions and agrees that Credit Suisse shall have no liability (whether direct or indirect) to the Company in respect of such a fiduciary duty claim or to any person asserting a fiduciary duty claim on behalf of or in right of the Company, including stockholders, employees or creditors of the Company.

15. Applicable Law. This Agreement shall be governed by, and construed in accordance with, the laws of the State of New York.

The Company hereby submits to the non-exclusive jurisdiction of the Federal and state courts in the Borough of Manhattan in The City of New York in any suit or proceeding arising out of or relating to this Agreement or the transactions contemplated hereby. The Company irrevocably and unconditionally waives any objection to the laying of venue of any suit or proceeding arising out of or relating to this

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Agreement or the transactions contemplated hereby in Federal and state courts in the Borough of Manhattan in The City of New York and irrevocably and unconditionally waives and agrees not to plead or claim in any such court that any such suit or proceeding in any such court has been brought in an inconvenient forum.

16. Integration. This Agreement constitutes the entire agreement of the parties to this Agreement and supersedes and replaces all prior written or oral and all contemporaneous oral agreements, understandings and negotiations with respect to the subject matter hereof.

[signature page follows]

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If the foregoing is in accordance with Credit Suisse’s understanding of our agreement, kindly sign and return to the Company one of the counterparts hereof, whereupon it will become a binding agreement between the Company and Credit Suisse in accordance with its terms.

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SCHEDULE A

None.

Number of Firm Securities: 13,000,000 shares

Number of Optional Securities: Not more than 1,950,000 shares

SCHEDULE B

List of Subsidiaries

Amylin Investments LLC

Amylin Ohio LLC