REGISTRATION RIGHTS AGREEMENT Dated as of February 4, 2005 between AMPHASTAR PHARMACEUTICALS, INC. and LOTUS CHINA FUND, L.P.

Exhibit 10.11

REGISTRATION RIGHTS AGREEMENT

Dated as of February 4, 2005

between

AMPHASTAR PHARMACEUTICALS, INC.

and

LOTUS CHINA FUND, L.P.

TABLE OF CONTENTS

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REGISTRATION RIGHTS AGREEMENT

THIS REGISTRATION RIGHTS AGREEMENT (the “Agreement”) is made as of the 4th day of February, 2005, by and between Amphastar Pharmaceuticals, Inc., a Delaware corporation (the “Company”), and Lotus China Fund, L.P. a Cayman Islands limited partnership (the “Investor”).

RECITALS

WHEREAS, pursuant to that certain Subscription Agreement between the Company and the Investor dated as of even date herewith (the “Subscription Agreement”), the Company has agreed to sell and issue to the Investor, and the Investor has agreed to purchase from the Company 675,676 shares of the Company’s Common Stock (the “Shares”); and

WHEREAS, in order to induce the Company to enter into the Subscription Agreement and to induce the Investor to invest funds in the Company pursuant to the Subscription Agreement, the Investor and the Company hereby agree that this Agreement shall govern the rights of the Investor to cause the Company to register shares of Common Stock issued to the Investor and certain other matters as set forth in this Agreement.

NOW, THEREFORE, THE PARTIES HEREBY AGREE AS FOLLOWS:

1. Definitions. For purposes of this Agreement:

1.1.         The term “Affiliate” shall mean with respect to any individual, corporation, partnership, association, trust, or any other entity (in each case, a “Person”), any Person which, directly or indirectly, controls, is controlled by or is under common control with such Person, including, without limitation any general partner, officer or director of such Person and any venture capital fund now or hereafter existing which is controlled by or under common control with one or more general partners or shares the same management company with such Person.

1.2.         The term “Common Stock” shall mean shares of the Company’s common stock, par value $0.0001 per share.

1.3.         The term “Exchange Act” shall mean the Securities Exchange Act of 1934, as amended, and the rules and regulations promulgated thereunder.

1.4.         The term “Form S-3” means such form under the Securities Act as in effect on the date hereof or any registration form under the Securities Act subsequently adopted by the SEC which permits inclusion or incorporation of substantial information by reference to other documents filed by the Company with the SEC.

1.5.         The term “GAAP” shall mean generally accepted accounting principles.

1.6.         The term “Holder” shall mean the Investor and any transferee of Registrable Securities in accordance with Section 2.7 hereof.

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1.7.                            The term “IPO” means the Company’s first underwritten public offering of its Common Stock under the Securities Act.

1.8.                            The term “register,” “registered,” and “registration” refer to a registration effected by preparing and filing a registration statement or similar document in compliance with the Securities Act, and the declaration or ordering of effectiveness of such registration statement or document.

1.9.                            The term “Registrable Securities” means (i) the Shares and, if any, the Additional Shares (as defined in the Subscription Agreement), (ii) securities issued or issuable upon any stock split, stock dividend, recapitalization or similar event with respect to the Shares; and (iii) any other security issued as a dividend or other distribution with respect to, in exchange for or in replacement of the securities referred to in the preceding clauses.

1.10.                     The term “SEC” means the Securities and Exchange Commission.

1.11.                     The term “SEC Rule 144” means Rule 144 promulgated by the SEC under the Securities Act.

1.12.                     The term “SEC Rule 144(k)” means Rule 144(k) promulgated by the SEC under the Securities Act.

1.13.                     The term “SEC Rule 145” means Rule 145 promulgated by the SEC under the Securities Act.

1.14.                     The term “Securities Act” means the Securities Act of 1933, as amended, and the rules and regulations promulgated thereunder.

1.15.                     The term “Violation” means losses, claims, damages, or liabilities (joint or several) to which a party hereto may become subject under the Securities Act, the Exchange Act or other federal or state law, insofar as such losses, claims, damages, or liabilities (or actions in respect thereof) arise out of or are based upon any of the following statements, omissions or violations: (i) any untrue statement or alleged untrue statement of a material fact contained in such registration statement, including any preliminary prospectus or final prospectus contained therein or any amendments or supplements thereto, (ii) the omission or alleged omission to state therein a material fact required to be stated therein, or necessary to make the statements therein not misleading.

2. Registration Rights. The Company covenants and agrees as follows:

2.1.                            Company Registration. If at any time after the IPO, the Company proposes to register (including for this purpose a registration effected by the Company for stockholders other than the Holder) any of its stock or other securities under the Securities Act in connection with the public offering of such securities solely for cash (other than a registration statement relating either to the sale of securities to employees of the Company pursuant to a stock option, stock purchase or similar plan or an SEC Rule 145 transaction, a registration on any form which does not include substantially the same information as would be required to be included in a registration statement covering the sale of the Registrable Securities or a

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registration in which the only Common Stock being registered is Common Stock issuable upon conversion of debt securities which are also being registered), the Company shall, at such time, promptly give each Holder written notice of such registration. Upon the written request of each Holder given within twenty (20) days after mailing of such notice by the Company in accordance with Section 3.5, the Company shall, subject to the provisions of Section 2.5, cause to be registered under the Securities Act all of the Registrable Securities that each such Holder has requested to be registered. The Company shall have the right to terminate or withdraw any registration initiated by it under this Section 2.1 prior to the effectiveness of such registration whether or not any Holder has elected to include securities in such registration. The expenses of such withdrawn registration shall be borne by the Company in accordance with Section 2.4 hereof.

2.2.                         Obligations of the Company. Whenever required under this Section 2 to effect the registration of any Registrable Securities, the Company shall, as expeditiously as reasonably possible,

(a)                                           prepare and file with the SEC a registration statement with respect to such Registrable Securities and use its reasonable commercial efforts to cause such registration statement to become effective, and, upon the request of the Holders of a majority of the Registrable Securities registered thereunder, keep such registration statement effective, subject to the exceptions below, for a period of up to ninety (90) days or, if earlier, until the distribution contemplated in the Registration Statement has been completed; provided, however, that such 90-day period shall be extended for a period of time equal to the period the Holder refrains from selling any securities included in such registration at the request of an underwriter of Common Stock (or other securities) of the Company or if the Company shall furnish to the Holders a certificate signed by the Chief Executive Officer of the Company that in the good faith judgment of the Board of Directors of the Company it could be detrimental to the Company and its shareholders for the registration statement to be in effect at such time;

(b)                                           prepare and file with the SEC such amendments and supplements to such registration statement and the prospectus used in connection with such registration statement as may be necessary to comply with the provisions of the Securities Act with respect to the disposition of all securities covered by such registration statement;

(c)                                            furnish to the Holders such numbers of copies of a prospectus, including a preliminary prospectus, in conformity with the requirements of the Securities Act, and such other documents as they may reasonably request in order to facilitate the disposition of Registrable Securities owned by them;

(d)                                           use its reasonable commercial efforts to register and qualify the securities covered by such registration statement under such other securities or Blue Sky laws of such jurisdictions as shall be reasonably requested by the Holders; provided that the Company shall not be required in connection therewith or as a condition thereto to qualify to do business or to file a general consent to service of process in any such states or jurisdictions, unless the Company is already subject to service in such jurisdiction and except as may be required by the Securities Act;

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(e)                                       in the event of any underwritten public offering, enter into and perform its obligations under an underwriting agreement, in usual and customary form, with the managing underwriter of such offering. Each Holder participating in such underwriting shall also enter into and perform its obligations under such an agreement;

(f)                                        cause all such Registrable Securities registered pursuant to this Agreement hereunder to be listed on a national securities exchange or trading system and each securities exchange and trading system on which similar securities issued by the Company are then listed;

(g)                                       provide a transfer agent and registrar for all Registrable Securities registered pursuant hereunder and a CUSIP number for all such Registrable Securities, in each case not later than the effective date of such registration;

(i)                                          use its reasonable commercial efforts to furnish, at the request of any Holder requesting registration of Registrable Securities pursuant to this Section 2, on the date on which such Registrable Securities are sold to the underwriter, (i) an opinion, dated such date, of the counsel representing the Company for the purposes of such registration, in form and substance as is customarily given to underwriters in an underwritten public offering, addressed to the underwriters, if any, and (ii) a “comfort” letter dated such date, from the independent certified public accountants of the Company, in form and substance as is customarily given by independent certified public accountants to underwriters in an underwritten public offering, addressed to the underwriters, if any.

2.3.                            Furnish Information. It shall be a condition precedent to the obligations of the Company to take any action pursuant to this Section 2 with respect to the Registrable Securities of any selling Holder that such Holder shall furnish to the Company such information regarding itself, the Registrable Securities held by it, and the intended method of disposition of such securities as shall be reasonably required to effect the registration of such Holder’s Registrable Securities.

2.4.                            Expenses of Company Registration. The Company shall bear and pay all expenses incurred in connection with any registration, filing or qualification of Registrable Securities with respect to the registrations pursuant to Section 2.1 hereof for each Holder (which right may be assigned as provided in Section 2.7 hereof), including (without limitation) all registration, filing, and qualification fees, printers and accounting fees relating or apportionable thereto and the fees and disbursements, not to exceed $25,000, of one counsel for the selling Holders selected by them (which counsel shall be reasonably acceptable to the Company), but excluding underwriting discounts and commissions relating to Registrable Securities.

2.5.                            Underwriting Requirements. In connection with any offering involving an underwriting of shares of the Company’s capital stock pursuant to this Section 2, the Company shall not be required to include any of the Holders’ securities in such underwriting unless they accept the terms of the underwriting as agreed upon between the Company and its underwriters, and then only in such quantity as the underwriters determine in their sole discretion will not jeopardize the success of the offering by the Company. If the total number of securities,

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including Registrable Securities, requested by stockholders to be included in such offering exceeds the amount of securities to be sold other than by the Company that the underwriters determine in their sole discretion is compatible with the success of the offering, then the Company shall be required to include in the offering only that number of such securities, including Registrable Securities, which the underwriters and the Company determine in their sole discretion will not jeopardize the success of the offering. Notwithstanding any other provision of this Section 2.5, if the managing underwriter determines that there be a limitation of the number of shares to be underwritten, no securities to be registered for sale by Holders shall be included unless all shares to be registered for sale by the Company to be included in such underwriting are so included and any remaining securities to be included in such registration shall be allocated pro rata among the Holders and any other holders of “piggy-back” registration rights (and no other stockholders), based on the number of shares requested to be included in such registration by all such holders. The Company shall so advise each Holder and the number of shares of Registrable Securities to be included in the registration and underwriting shall be so limited. For purposes of apportionment as set forth in this Section 2.5, for any selling stockholder which is a Holder of Registrable Securities and which is an investment fund, partnership, limited liability company or corporation, the partners, members, retired partners, retired members, stockholders and Affiliates of such Holder, or the estates and family members of any such partners, retired partners, members and retired members and any trusts for the benefit of any of the foregoing persons shall be deemed to be a single “selling Holder”, and any pro-rata reduction with respect to such “selling Holder” shall be based upon the aggregate amount of shares carrying registration rights owned by all entities and individuals included in such “selling Holder,” as defined in this sentence.

2.6.                            Delay of Registration. No Holder shall have any right to obtain or seek an injunction restraining or otherwise delaying any registration pursuant to this Agreement as the result of any controversy that might arise with respect to the interpretation or implementation of this Section 2.

2.7.                            Assignment of Registration Rights. The registration rights of any Holder (and of any permitted transferee of any Holder or such Holder’s permitted transferees) under this Agreement with respect to any Registrable Securities may be transferred to any transferee who acquires at least 100,000 Registrable Securities (such number to be adjusted appropriately for stock splits, stock dividends, recapitalizations and the like) (otherwise than in a registered public offering or in any sale under Rule 144 under the Securities Act) and executes an instrument agreeing to be bound by this Agreement. The Holder shall give written notice to the Company promptly after any such transfer stating the name and address of the transferee and identifying the securities with respect to which the rights under this Agreement are being assigned.

2.8.                            “Market Stand-Off’ Agreement. Each Holder hereby agrees that it will not, without the prior written consent of the managing underwriter, during the period commencing on the date of the final prospectus relating to the Company’s IPO and ending on the date specified by the Company and the managing underwriter (such period not to exceed one hundred eighty (180) days, plus under certain circumstances, an additional 18-day period if the Company issues an earnings release or material news or event relating to the Company occurs during the last 17 days of the 180-day restricted period) (i) lend, offer, pledge, sell, contract to

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sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, hedge, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock (whether such shares or any such securities are then owned by the Holder or are thereafter acquired), (ii) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (i) or (ii) above is to be settled by delivery of Common Stock or other securities, in cash or otherwise, or (iii) publicly announce the intention to take any of the actions described in (i) or (ii) of this Section 2.8. The foregoing provisions of this Section 2.8 shall apply to the Company’s IPO, shall not apply to the sale of any shares to an underwriter pursuant to an underwriting agreement, and shall only be applicable to the Holders if all executive officers, directors and greater than 5% stockholders of the Company enter into similar agreements. The underwriters in connection with the Company’s IPO are intended third-party beneficiaries of this Section 2.8 and shall have the right, power and authority to enforce the provisions hereof as though they were a party hereto. Each Holder further agrees to execute such agreements as may be reasonably requested by the underwriters in the Company’s IPO that are consistent with this Section 2.8 or that are necessary to give further effect thereto.

In order to enforce the foregoing covenant, the Company may impose stop-transfer instructions with respect to the Registrable Securities of each Holder (and the shares or securities of every other person subject to the foregoing restriction) until the end of such period.

2.9.                            Indemnification.   In the event any Registrable Securities are included in a registration statement under this Section 2:

(a)                   To the extent permitted by law, the Company will indemnify and hold harmless each Holder, the partners, members, officers, directors and stockholders of each Holder, and each person, if any, who controls such Holder within the meaning of the Securities Act or the Exchange Act, against any Violation and the Company will reimburse each such Holder, or other aforementioned person, for any legal or other expenses reasonably incurred by them in connection with investigating or defending any such loss, claim, damage, liability, or action as such expenses are incurred; provided, however, that the indemnity agreement contained in this subsection 2.9(a) shall not apply to amounts paid in settlement of any such loss, claim, damage, liability, or action if such settlement is effected without the consent of the Company (which consent shall not be unreasonably withheld), nor shall the Company be liable in any such case for any such loss, claim, damage, liability, or action to the extent that it arises out of or is based upon a Violation which occurs in reliance upon and in conformity with written information furnished expressly for use in connection with such registration by any such Holder or other aforementioned person.

(b)                   To the extent permitted by law, each selling Holder will severally and not jointly indemnify and hold harmless the Company, each of its directors, each of its officers who has signed the registration statement, each person, if any, who controls the Company within the meaning of the Securities Act, and any other Holder selling securities in such registration statement against any losses, claims, damages, or liabilities (joint or several) to

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which any of the foregoing persons may become subject, under the Securities Act, the Exchange Act or other federal or state law, insofar as such losses, claims, damages, or liabilities (or actions in respect thereto) arise out of or are based upon any Violation, in each case to the extent (and only to the extent) that such Violation occurs in reliance upon and in conformity with written information furnished by such Holder expressly for use in connection with such registration; and each such Holder will reimburse, any legal or other expenses reasonably incurred by any person intended to be indemnified pursuant to this subsection 2.9(b), in connection with investigating or defending any such loss, claim, damage, liability, or action; provided, however, that the indemnity agreement contained in this subsection 2.9(b) shall not apply to amounts paid in settlement of any such loss, claim, damage, liability or action if such settlement is effected without the consent of the Holder, which consent shall not be unreasonably withheld; provided, further, that, in no event shall any indemnity under this subsection 2.9(b) exceed the net proceeds from the offering received by such Holder, except in the case of fraud or willful misconduct by such Holder.

(c)                    Promptly after receipt by an indemnified party under this Section 2.9 of notice of the commencement of any action (including any governmental action), such indemnified party will, if a claim in respect thereof is to be made against any indemnifying party under this Section 2.9, deliver to the indemnifying party a written notice of the commencement thereof and the indemnifying party shall have the right to participate in, and, to the extent the indemnifying party so desires, jointly with any other indemnifying party similarly noticed, to assume the defense thereof with counsel mutually satisfactory to the parties; provided, however, that an indemnified party (together with all other indemnified parties which may be represented without conflict by one counsel) shall have the right to retain one separate counsel, with the fees and expenses to be paid by the indemnifying party, if representation of such indemnified party by the counsel retained by the indemnifying party would be inappropriate due to actual or potential differing interests between such indemnified party and any other party represented by such counsel in such proceeding. The failure to deliver written notice to the indemnifying party within a reasonable time of the commencement of any such action, if prejudicial to its ability to defend such action, shall relieve such indemnifying party of any liability to the indemnified party under this Section 2.9, but only to the extent that said indemnifying party is prejudiced with respect thereto, but the omission so to deliver written notice to the indemnifying party will not relieve it of any liability that it may have to any indemnified party otherwise than under this Section 2.9.

(d)                   In order to provide for just and equitable contribution to joint liability under the Securities Act in any case in which either (i) any Holder exercising rights under this Agreement, or any controlling person of any such Holder, makes a claim for indemnification pursuant to this Section 2.9 but it is judicially determined (by the entry of a final judgment or decree by a court of competent jurisdiction and the expiration of time to appeal or the denial of the last right of appeal) that such indemnification may not be enforced in such case notwithstanding the fact that this Section 2.9 provides for indemnification in such case, or (ii) contribution under the Securities Act may be required on the part of any such selling Holder or any such controlling person in circumstances for which indemnification is provided under this Section 2.9, then, and in each such case, the Company and such Holder will contribute to the aggregate losses, claims, damages or liabilities to which they may be subject (after contribution from others) in such proportion as is appropriate to reflect the relative fault of the indemnifying

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party on the one hand and of the indemnified party on the other in connection with the statements or omissions that resulted in such loss, liability, claim, damage, or expense as well as any other relevant equitable considerations. The relative fault of the indemnifying party and of the indemnified party 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 indemnifying party or by the indemnified party and the parties’ relative intent, knowledge, access to information, and opportunity to correct or prevent such statement or omission; provided however, that, in any such case, (I) no such Holder will be required to contribute any amount in excess of the public offering price of all such Registrable Securities offered and sold by such Holder pursuant to such registration statement, and (II) no person or entity guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Securities Act) will be entitled to contribution from any person or entity who was not guilty of such fraudulent misrepresentation; provided further, that in no event shall a Holder’s liability pursuant to this Section 2.9(d), when combined with the amounts paid or payable by such holder pursuant to Section 2.9(b), exceed the proceeds from the offering (net of any underwriting discounts or commissions) received by such Holder, except in the case of willful fraud by such Holder.

(e)                    Notwithstanding the foregoing, to the extent that the provisions on indemnification and contribution contained in the underwriting agreement entered into in connection with the underwritten public offering are in conflict with the foregoing provisions, the provisions in the underwriting agreement shall control.

(f)                     Unless otherwise superceded by an underwriting agreement entered into in connection with the underwritten public offering, the obligations of the Company and Holders under this Section 2.9 shall survive the completion of any offering of Registrable Securities in a registration statement under this Section 2, and otherwise shall survive the termination of this Agreement.

2.10.                     Termination of Registration Rights.

(a)                                           No Holder shall be entitled to exercise any right provided for in this Section 2 after three (3) years following the consummation of the IPO.

(b)                                           The rights set forth in this Section 2 shall terminate as to any Holder, when the Registrable Securities held by such Holder (together with any Affiliate of such Holder with whom such Holder must aggregate its sales under SEC Rule 144) could be sold without restriction under SEC Rule 144(k) within a ninety (90) day period.

3. Miscellaneous.

3.1.                            Transfers, Successors and Assigns. The terms and conditions of this Agreement shall inure to the benefit of and be binding upon the respective permitted successors and assigns of the parties. Nothing in this Agreement, express or implied, is intended to confer upon any party other than the parties hereto or their respective permitted successors and assigns any rights, remedies, obligations, or liabilities under or by reason of this Agreement, except as expressly provided in this Agreement.

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3.2.                            Governing Law. This Agreement shall be governed by and construed in accordance with the General Corporation Law of the State of Delaware as to matters within the scope thereof, and as to all other matters shall be governed by and construed in accordance with the internal laws of the State of California, without regard to its principles of conflicts of laws.

3.3.                            Counterparts. This Agreement may be executed in two or more counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same instrument. This Agreement may also be executed and delivered by facsimile signature and in two or more counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same instrument.

3.4.                            Titles and Subtitles. The titles and subtitles used in this Agreement are used for convenience only and are not to be considered in construing or interpreting this Agreement.

3.5.                            Notices. All notices and other communications given or made pursuant to this Agreement shall be in writing and shall be deemed effectively given: (a) upon personal delivery to the party to be notified, (b) when sent by confirmed electronic mail or facsimile if sent during normal business hours of the recipient, and if not so confirmed, then on the next business day, (c) five (5) days after having been sent by registered or certified mail, return receipt requested, postage prepaid, or (d) one (1) day after deposit with a nationally recognized overnight courier, specifying next day delivery, with written verification of receipt. All communications shall be sent to the respective parties at their address as set forth on the signature page hereto, or to such email address, facsimile number or address as subsequently modified by written notice given in accordance with this Section 3.5. If notice is given to the Company, a copy shall also be sent to:

Latham & Watkins

633 West Fifth Street, Suite 4000

Los Angeles, California 90071

Facsimile: (213) 891-8763

Attention: Cynthia A. Rotell

3.6.                            Amendments and Waivers. Any term of this Agreement may be amended and the observance of any term of this Agreement may be waived (either generally or in a particular instance and either retroactively or prospectively), only with the written consent of the Company and the holders of a majority of the Registrable Securities then outstanding. Any amendment or waiver effected in accordance with this paragraph shall be binding upon each holder of any Registrable Securities then outstanding, each future holder of all such Registrable Securities, and the Company. The Company shall give prompt written notice of any amendment or termination hereof or waiver hereunder to any party hereto that did not consent in writing to such amendment, termination or waiver. Any amendment, termination or waiver effected in accordance with this Section 3.6 shall be binding on all parties hereto, even if they do not execute such consent. No waivers of or exceptions to any term, condition or provision of this Agreement, in any one or more instances, shall be deemed to be, or construed as, a further or continuing waiver of any such term, condition or provision.

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3.7.                            Severability. The invalidity or unenforceability of any provision hereof shall in no way affect the validity or enforceability of any other provision.

3.8.                            Aggregation of Stock. All shares of Registrable Securities held or acquired by Affiliates shall be aggregated together for the purpose of determining the availability of any rights under this Agreement.

3.9.                            Entire Agreement. This Agreement (including the Exhibits hereto, if any) constitutes the full and entire understanding and agreement between the parties with respect to the subject matter hereof, and any other written or oral agreement relating to the subject matter hereof existing between the parties are expressly canceled.

3.10.                     Submission to Jurisdiction. With respect to any claim or unresolved controversy arising out of this Agreement, each of the parties to this Agreement consents to the personal jurisdiction of the U.S. District Court for the District of California or any court of the State of California having subject matter jurisdiction.

3.11.                     Delays or Omissions. No delay or omission to exercise any right, power or remedy accruing to any party under this Agreement, upon any breach or default of any other party under this Agreement, shall impair any such right, power or remedy of such non-breaching or non-defaulting party nor shall it be construed to be a waiver of any such breach or default, or an acquiescence therein, or of or in any similar breach or default thereafter occurring; nor shall any waiver of any single breach or default be deemed a waiver of any other breach or default theretofore or thereafter occurring. Any waiver, permit, consent or approval of any kind or character on the part of any party of any breach or default under this Agreement, or any waiver on the part of any party of any provisions or conditions of this Agreement, must be in writing and shall be effective only to the extent specifically set forth in such writing. All remedies, either under this Agreement or by law or otherwise afforded to any party, shall be cumulative and not alternative.

[Remainder of Page Intentionally Left Blank]

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IN WITNESS WHEREOF, the parties have executed this Agreement as of the date first above written.

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