WARRANT AGREEMENT To Purchase Shares of the Series C Preferred Stock of HORIZON THERAPEUTICS, INC. Dated as of December 18, 2007 (the Effective Date)

Exhibit 4.3

THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933 AS AMENDED, OR ANY STATE SECURITIES LAWS. THEY MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED, OR HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT RELATED THERETO OR AN OPINION OF COUNSEL (WHICH MAY BE COMPANY COUNSEL) REASONABLY SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED UNDER THE SECURITIES ACT OF 1933 ACT AS AMENDED, OR ANY APPLICABLE STATE SECURITIES LAWS.

WARRANT AGREEMENT

To Purchase Shares of the Series C Preferred Stock of

HORIZON THERAPEUTICS, INC.

Dated as of December 18, 2007 (the “Effective Date”)

WHEREAS, Horizon Therapeutics, Inc, (the “Company”), has entered into a Loan and Security Agreement of even date herewith (the “Loan Agreement”) with Comerica Bank (the “Warrantholder”);

WHEREAS, the Company desires to grant to Warrantholder, in consideration for, among other things, the financial accommodations provided for in the Loan Agreement, the right to purchase shares of its Series C Preferred Stack pursuant to this Warrant Agreement (the “Warrant”);

NOW, THEREFORE, in consideration of the Warrantholder executing and delivering the Loan Agreement and providing the financial accommodations contemplated therein, and in consideration of the mutual covenants and agreements contained herein, the Company and Warrantholder agree as follows:

SECTION 1. GRANT OF THE RIGHT TO PURCHASE WARRANT STOCK.

For value received, the Company hereby grants to the Warrantholder, and the Warrantholder is entitled, upon the terms and subject to the conditions hereinafter set forth, to subscribe for and purchase, from the Company, 5,626 fully paid and non-assessable shares of the Warrant Stock (as defined below) at a purchase price of $14.22 per share (the “Exercise Price”). The number and Exercise Price of such shares are subject to adjustment as provided in Section 8. As used herein, the following terms shall have the following meanings:

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

“Charter” means the Company’s Certificate of Incorporation, as may be amended from time to time.

“Common Stock” means the Company’s common stock;

“Initial Public Offering” means the initial underwritten public offering of the Company’s Common Stock pursuant to a registration statement under the Act, which public offering has been declared effective by the Securities and Exchange Commission (“SEC”);

“Merger Event” means a merger or consolidation involving the Company in which the Company is not the surviving entity, or in which the outstanding shares of the Company’s capital stock are otherwise converted into or exchanged for shares of capital of another entity, except for a merger effected exclusively for the purpose of changing the domicile of the Company or a consolidation with a wholly-owned subsidiary of the Company.

“Purchase Price” means, with respect to any exercise of this Warrant, an amount equal to the Exercise Price as of the relevant time multiplied by the number of shares of Warrant Stock requested to be exercised under this Warrant pursuant to such exercise.

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“Rights Agreement” means that certain Amended and Restated Investors’ Rights Agreement among the Company and certain of its shareholders dated as of July 19, 2007.

“Warrant Stock” means the Series C Preferred Stock of the Company and any other stock into or for which the Series C Preferred Stock may be converted or exchanged, and upon and after the occurrence of an event which results in the automatic or voluntary conversion, redemption or retirement of all (but not less than all) of the outstanding shares of such Series C Preferred Stock, including, without limitation, the consummation of an Initial Public Offering of the Common Stock in which such a conversion occurs, then from and after the date upon which such outstanding shares are so converted, redeemed or retired, “Warrant Stock” shall mean such Common Stock.

SECTION 2. TERM OF THE WARRANT.

Except as otherwise provided for herein, the term of this Warrant and the right to purchase Warrant Stock as granted herein shall commence on the Effective Date and shall be exercisable for a period ending upon the earliest to occur of (i) seven (7) years from the Effective Date; (ii) five (5) years after the Initial Public Offering; or (iii) the consummation of a Merger Event in which this Warrant is not assumed by the successor in such transaction and the consideration paid in such transaction consists of cash and/or securities of a class registered pursuant to Section 12(b) or 12(g) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”).

SECTION 3. EXERCISE OF THE PURCHASE RIGHTS.

(a) Exercise. The purchase rights set forth in this Warrant are exercisable by the Warrantholder, in whole or in part, at any time, or from time to time, prior to the expiration of the term set forth in Section 2, by tendering to the Company at its principal office a notice of exercise in the form attached hereto as Exhibit I (the “Notice of Exercise”), duly completed and executed. Promptly upon receipt of the Notice of Exercise and the payment of the Purchase Price in accordance with the terms set forth below, and in no event later than three (3) days thereafter, the Company shall issue to the Warrantholder a certificate for the number of shares of Warrant Stock purchased and shall execute the acknowledgment of exercise in the form attached hereto as Exhibit II (the “Acknowledgment of Exercise”) indicating the number of shares which remain subject to future purchases, if any.

(i) The Purchase Price may be paid at the Warrantholder’s election either by cash or check.

Upon partial exercise, the Company shall promptly issue an amended Warrant representing the remaining number of shares purchasable hereunder. All other terms and conditions of such amended Warrant shall be identical to those contained herein, including, but not limited to the Effective Date hereof.

(b) Treatment of Warrant in the Event of a Merger Event. The Company shall give Holder written notice at least 10 days prior to the closing of any proposed Merger Event. The Company will use commercially reasonable efforts to cause the acquirer of the Company under the Merger Event (the “Acquirer”) to assume this Warrant as a part of the Merger Event. (A) If the Acquirer assumes this Warrant, then this Warrant shall be exercisable for the same securities, cash and property as would be payable for the Warrant Stock issuable upon exercise of the unexercised portion of this Warrant as if such Warrant Stock were outstanding on the record date for the Acquisition and subsequent closing. The Warrant Price shall he adjusted accordingly, and the Warrant Price and number and class of Warrant Stock shall continue to be subject to adjustment from time to time in accordance with the provisions hereof. (B) If the Acquirer refuses to assume this Warrant in connection with the Merger Event and the consideration paid in such transaction consists of cash and/or securities of a class registered pursuant to Section 12(b) or 12(g) of the Act, the Company shall give Holder an additional written notice at least 5 days prior to the closing of the Merger Event of such fact. In such event, notwithstanding any other provision of this Warrant to the contrary, Holder may immediately exercise this Warrant in the manner specified in this Warrant with such exercise effective immediately prior to closing of the Merger Event. If Holder elects not to exercise this Warrant, then this Warrant will terminate immediately prior to the closing of the Merger Event.

SECTION 4. RESERVATION OF SHARES.

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During the term of this Warrant, the Company will at all times have authorized and reserved a sufficient number of shares of its Warrant Stock to provide for the exercise of the rights to purchase Warrant Stock as provided for herein, and shall have authorized and reserved a sufficient number of shares of its Common Stock to provide for the conversion of the Warrant Stock available hereunder.

SECTION 5. NO FRACTIONAL SHARES OR SCRIP.

No fractional shares or scrip representing fractional shares shall be issued upon the exercise of this Warrant, but in lieu of such fractional shares the Company shall make a cash payment therefor upon the basis of the Exercise Price then in effect.

SECTION 6. NO RIGHTS AS STOCKHOLDER.

This Warrant does not entitle the Warrantholder to any voting rights or other rights as a stockholder of the Company prior to the exercise of this Warrant.

SECTION 7. WARRANTHOLDER REGISTRY.

The Company shall maintain a registry showing the name and address of the registered holder of this Warrant. Warrantholder’s initial address, for purposes of such registry, is set forth below Warrantholder’s signature on this Warrant. Warrantholder may change such address by giving written notice of such changed address to the Company.

SECTION 8. ADJUSTMENT RIGHTS.

The Exercise Price and the number of shares of Warrant Stock purchasable hereunder are subject to adjustment, as follows:

(a) Merger Event. (i) If the successor or surviving entity in a Merger Event assumes this Warrant, then this Warrant shall be exercisable for the same securities, cash, and property as would be payable for the Warrant Stock issuable upon exercise of the unexercised portion of this Warrant as if such Warrant Stock were outstanding on the record date for the Merger Event and subsequent closing. The Exercise Price shall be adjusted accordingly, and the Exercise Price and number and class of Warrant Stock shall continue to be subject to adjustment from time to time in accordance with the provisions hereof.

(ii) If the consideration in such Merger Event is cash and/or securities of a class registered pursuant to Section 12(b) or 12(g) of the Exchange Act, then the successor or surviving entity may elect not to assume this Warrant, in which case, unless the Warrantholder has otherwise exercised this Warrant, then effective immediately prior to the closing of such Merger Event, this Warrant shall be automatically exercised pursuant to Section 3(b) above.

(b) Reclassification of Shares. Except as set forth in section 8(a), if the Company at any time shall, by combination, reclassification, exchange or subdivision of securities or otherwise, change any of the securities as to which purchase rights under this Warrant exist into the same or a different number of securities of any other class or classes, this Warrant shall thereafter represent the right to acquire such number and kind of securities as would have been issuable as the result of such change with respect to the securities which were subject to the purchase rights under this Warrant immediately prior to such combination, reclassification, exchange, subdivision or other change.

(c) Subdivision or Combination of Shares. if the Company at any time shall combine or subdivide its Warrant Stock, (i) in the case of a subdivision, the Exercise Price shall be proportionately decreased, and the number of shares of Warrant Stock issuable upon exercise of this Warrant shall be proportionately increased, or (ii) in the case of a combination, the Exercise Price shall be proportionately increased, and the number of shares of Warrant Stock issuable upon the exercise of this Warrant shall be proportionately decreased.

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(d) Stock Dividends. If the Company at any time while this Warrant is outstanding and unexpired shall:

(i) pay a dividend with respect to the Warrant Stock payable in Warrant Stock, then the Exercise Price shall be adjusted, from and after the date of determination of stockholders entitled to receive such dividend or distribution, to that price determined by multiplying the Exercise Price in effect immediately prior to such date of determination by a fraction (A) the numerator of which shall be the total number of shares of Warrant Stock outstanding immediately prior to such dividend or distribution, and (B) the denominator of which shall be the total number of shares of Warrant Stock outstanding immediately after such dividend or distribution; or

(ii) make any other distribution with respect to Warrant Stock (or stock into which the Warrant Stock is convertible), except any distribution specifically provided for in any other clause of this Section 8, then, in each such case, provision shall be made by the Company such that the Warrantholder shall receive upon exercise or conversion of this Warrant a proportionate share of any such distribution as though it were the holder of the Warrant Stock (or other stock for which the Warrant Stock is convertible) as of the record date fixed for the determination of the stockholders of the Company entitled to receive such distribution.

(e) Antidilution Rights. Additional antidilution rights applicable to the Warrant Stock purchasable hereunder are as set forth in the Company’s Charter and shall be applicable with respect to the Warrant Stock issuable hereunder. The Company shall promptly provide the Warrantholder with any restatement, amendment, modification or waiver of the Charter; provided, that no such amendment, modification or waiver shall impair or reduce the antidilution rights applicable to the Warrant Stock as of the date hereof unless such amendment, modification or waiver affects the rights of Warrantholder with respect to the Warrant Stock in the same manner as it affects all other holders of Warrant Stock, The Company shall provide Warrantholder with prompt written notice after any issuance of any equity security issued in a bona fide financing after the Effective Date of this Warrant, which notice shall include (a) the price at which such stock or security was sold, (b) the number of shares issued, and (c) such other information as necessary for Warrantholder to determine if a dilutive event has occurred. For the avoidance of doubt, there shall be no duplicate anti-dilution adjustment pursuant to this subsection (e), the forgoing subsection (d) and the Company’s Charter.

(f) Notice of Adjustments. If: (i) the Company shall declare any dividend or distribution upon its stock, whether in stock, cash, property or other securities; (ii) there shall be any Merger Event; (iv) there shall be an Initial Public Offering; (iv) the Company shall sell, lease, license or otherwise transfer all or substantially all of its assets; or (v) there shall be any voluntary dissolution, liquidation or winding up of the Company; then, in connection with each such event, the Company shall send to the Warrantholder: (A) at least ten (10) days’ prior written notice of the date on which the books of the Company shall close or a record shall be taken for such dividend or distribution (specifying the date on which the holders of Warrant Stock shall be entitled thereto) or for determining rights to vote in respect of such Merger Event, dissolution, liquidation or winding up; and (B) in the case of any such Merger Event, sale, lease, license or other transfer of all or substantially all assets, dissolution, liquidation or winding up, at least ten (10) days’ prior written notice of the date when the same shall take place (and specifying the date on which the holders of Warrant Stock shall be entitled to exchange their Warrant Stock for securities or other property deliverable upon such Merger Event, dissolution, liquidation or winding up).

Each such written notice shall set forth, in reasonable detail, (i) the event requiring the notice, and (ii) if any adjustment is required to be made, (A) the amount of such adjustment, (B) the method by which such adjustment was calculated, (C) the adjusted Exercise Price (if the Exercise Price has been adjusted), and (D) the number of shares subject to purchase hereunder after giving effect to such adjustment, and shall be given by first class mail, postage prepaid, or by reputable overnight courier with all charges prepaid, addressed to the Warrantholder at the address for Warrantholder set forth in the registry referred to in Section 7.

(g) Timely Notice. Failure to provide such notice required by subsection (f) above shall entitle Warrantholder to retain the benefit of the applicable notice period notwithstanding anything to the contrary contained in any insufficient notice received by Warrantholder. For purposes of this subsection (g), and

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notwithstanding anything to the contrary in Section 12(g), the notice period shall begin on the date Warrantholder actually receives a written notice containing all the information required to be provided in such subsection (f).

SECTION 9. REPRESENTATIONS, WARRANTIES AND COVENANTS OF THE COMPANY.

(a) Reservation of Warrant Stock. The Warrant Stock issuable upon exercise of the Warrantholder’s rights has been duly and validly reserved and, when issued in accordance with the provisions of this Warrant, will be validly issued, fully paid and non-assessable, and will be free of any taxes, liens, charges or encumbrances of any nature whatsoever (other than those created or imposed pursuant to the Loan Agreement); provided, that the Warrant Stock issuable pursuant to this Warrant may be subject to restrictions on transfer under state and/or federal securities laws. The Company has made available to the Warrantholder true, correct and complete copies of its Charter and current bylaws. The issuance of certificates for shares of Warrant Stock upon exercise of this Warrant shall be made without charge to the Warrantholder for any issuance tax in respect thereof, or other cost incurred by the Company in connection with such exercise and the related issuance of shares of Warrant Stock; provided, that the Company shall not be required to pay any tax which may be payable in respect of any transfer and the issuance and delivery of any certificate in a name other than that of the Warrantholder.

(b) Due Authority. The execution and delivery by the Company of this Warrant and the performance of all obligations of the Company hereunder, including the issuance to Warrantholder of the right to acquire the shares of Warrant Stock and the Common Stock into which it may be converted, have been duly authorized by all necessary corporate action on the part of the Company. This Warrant: (1) is not inconsistent with the Company’s Charter or current bylaws; (2) does not contravene any law or governmental rule, regulation or order applicable to it; and (3) does not and will not contravene any provision of, or constitute a default under, any indenture, mortgage, contract or other instrument to which it is a party or by which it is bound. This Warrant constitutes a legal, valid and binding agreement of the Company, enforceable in accordance with its terms except (i) as limited by applicable bankruptcy, insolvency, reorganization, moratorium, fraudulent conveyance, or other laws of general application relating to or affecting the enforcement of creditors’ rights generally or (ii) as limited by laws relating to the availability of specific performance, injunctive relief, or other equitable remedies.

(c) Consents and Approvals. No consent or approval of, giving of notice to, registration with, or taking of any other action in respect of any state, federal or other governmental authority or agency is required with respect to the execution, delivery and performance by the Company of its obligations under this Warrant, except for the filing of notices pursuant to Regulation D under the Act and any filing required by applicable state securities law, which filings will be effective by the time required thereby.

(d) Issued Securities. All issued and outstanding shares of Common Stock, Preferred Stock or any other securities of the Company have been duly authorized and validly issued and are fully paid and nonassessable. All outstanding shares of Common Stock, Preferred Stock and any other securities were issued in full compliance with all federal and state securities laws. In addition, as of the date immediately preceding the date of this Warrant:

(i) The authorized capital of the Company consists of (A) 8,000,000 shares of Common Stock, of which 1,999,999 shares are issued and outstanding, (B) 1,192,118 shares of Series A Preferred Stock, all of which shares are issued and outstanding and are convertible into 1,192,118 shares of Common Stock, (C) 1,482,213 shares of Series B Preferred Stock, all of which shares are issued and outstanding and are convertible into 1,482,213 shares of Common Stock, and (D) 2,200,000 shares of Series C Preferred Stock, of which 2,109,706 shares are issued and outstanding and are convertible into 2,109,706 shares of Common Stock.

(ii) The Company has reserved 250,000 shares of Common Stock for issuance under its Stock Option Plan(s), under which 100,000 options are outstanding. Except for (a) the conversion privileges described in Section 9(d)(i) above and (b) the rights provided in the Rights Agreement, there are no other options, warrants, conversion privileges or other rights presently outstanding to purchase or otherwise acquire any authorized but unissued shares of the Company’s capital stock or other securities of the Company. The Company has no outstanding loans to any employee, officer or director of the Company, and the Company agrees not to enter into any such loan or otherwise guarantee the payment of any loan made to an employee, officer or director by a third party.

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(e) Insurance. The Company has in full force and effect insurance policies, with extended coverage, insuring the Company and its property and business against such losses and risks, and in such amounts, as are customary for corporations engaged in a similar business and similarly situated and as otherwise may be required pursuant to the terms of any other contract or agreement.

(f) Other Commitments to Register Securities. Except as set forth in this Warrant and in the Rights Agreement, the Company is not, pursuant to the terms of any other agreement currently in existence, under any obligation to register under the Act any of its presently outstanding securities or any of its securities which may hereafter be issued.

(g) Exempt Transaction. Subject to the accuracy of the Warrantholder’s representations in Section 10, the issuance of the Warrant Stock upon exercise of this Warrant, and the issuance of the Common Stock upon conversion of the Warrant Stock, will each constitute a transaction exempt from (i) the registration requirements of Section 5 of the Act, in reliance upon Section 4(2) thereof, and (ii) the qualification requirements of the applicable state securities laws.

(h) Compliance with Rule 144. If, after the effective date of the first registration statement filed by the Company, the Warrantholder proposes to sell Warrant Stock issuable upon the exercise of this Warrant, or the Common Stock into which it is convertible, in compliance with Rule 144 promulgated by the SEC, then, upon Warrantholder’s written request to the Company, the Company shall furnish to the Warrantholder, within ten days after receipt of such request, a written statement confirming the Company’s compliance with the filing requirements of the SEC as set forth in such Rule, as such Rule may be amended from time to time.

(i) Information Rights. During the term of this Warrant and until the Company’s initial public offering or a Merger Event, Warrantholder shall be entitled to the information rights contain in Section 7.1 of the Loan Agreement (other than Section 7.1(e) and (f)), and Section 7.1 of the Loan Agreement is hereby incorporated into this Warrant by this reference as though fully set forth herein, provided, however, that the Company shall not be required to deliver a Compliance Certificate once all Indebtedness (as defined in the Loan Agreement) owed by the Company to Warrantholder as been repaid. All information will be Confidential Information subject to Section 11.2 of the Loan Agreement, which is hereby incorporated into this Warrant by this reference as though fully set forth herein and is binding on Holder as if it were a Lender thereunder.

SECTION 10. REPRESENTATIONS AND COVENANTS OF THE WARRANTHOLDER.

This Warrant has been entered into by the Company in reliance upon the following representations and covenants of the Warrantholder:

(a) Investment Purpose. The right to acquire Warrant Stock or the Warrant Stock issuable upon exercise of the Warrantholder’s rights contained herein will be acquired for investment and not with a view to the sale or distribution of any part thereof, and the Warrantholder has no present intention of selling or engaging in any public distribution of the same except pursuant to a registration or exemption.

(b) Private Issue. The Warrantholder understands (i) that the Warrant Stock issuable upon exercise of this Warrant is not registered under the Act or qualified under applicable state securities laws on the ground that the issuance contemplated by this Warrant will be exempt from the registration and qualifications requirements thereof, and (ii) that the Company’s reliance on such exemption is predicated on the representations set forth in this Section 10.

(c) Financial Risk. The Warrantholder has such knowledge and experience in financial and business matters as to be capable of evaluating the merits and risks of its investment, and has the ability to bear the economic risks of its investment.

(d) Risk of No Registration. The Warrantholder understands that if the Company does not register with the SEC pursuant to Section 12 of the Securities Exchange Act of 1934 (the “1934 Act”), or file reports pursuant to Section 15(d) of the 1934 Act, or if a registration statement covering the securities under the Act is not

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in effect when it desires to sell (i) the rights to purchase Warrant Stock pursuant to this Warrant or (ii) the Warrant Stock issuable upon exercise of the right to purchase, it may be required to hold such securities for an indefinite period. The Warrantholder also understands that any sale of (A) its rights hereunder to purchase Warrant Stock or (B) Warrant Stock issued or issuable hereunder which might be made by it in reliance upon Rule 144 under the Act may be made only in accordance with the terms and conditions of that Rule.

(e) Accredited Investor. Warrantholder is an “accredited investor” within the meaning of the Securities and Exchange Rule 501 of Regulation D, as presently in effect.

(f) Lock-Up Agreement.

(i) Lock-Up Period; Agreement. In connection with the initial public offering of the Company’s securities and upon request of the Company or the underwriters managing such offering of the Company’s securities, Warrantholder agrees not to sell, make any short sale of, loan, grant any option for the purchase of, or otherwise dispose of any of the Company’s Common Stock (or any securities convertible into the Company’s Common Stock), however or whenever acquired (other than those included in the registration or purchased subsequent to the initial public offering) without the prior written consent of the Company or such underwriters, as the case may he, for such period of time (not to exceed 180 days, but subject to such extension or extensions as may be required by the underwriters in order to publish research reports while complying with the Rule 2711 of the National Association of Securities Dealers, Inc., such extension or extensions not to exceed 18 days after the expiration of such 180-day period) from the effective date of such registration statement as may be requested by the Company or such managing underwriters and to execute an agreement reflecting the foregoing as may be requested by the underwriters at the time of the Company’s initial public offering.

(ii) The obligations described in Section 10(f)(i) shall apply only if all officers and directors of the Company, and all holders of the Company’s outstanding securities are bound by agreements at least as restrictive as the terms of Section 10(f)(i).

(iii) in order to enforce the foregoing covenants, the Company may impose stop-transfer instructions with respect to the securities of the Warrantholder.

(iv) The Warrantholder agrees that it will not transfer securities of the Company unless each transferee agrees in writing to be bound by all of the provisions of this Section 10(f).

(v) The Warrantholder agrees that a legend reading substantially as follows shall be placed on all certificates representing all shares of Common Stock issued or issuable upon conversion of the Warrant Stock issuable upon exercise of this Warrant:

THE SECURITIES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO A LOCK-UP PERIOD OF UP TO 180 DAYS (BUT SUBJECT TO AN EXTENSION IN CERTAIN CIRCUMSTANCES NOT TO EXCEED 18 DAYS) AFTER THE EFFECTIVE DATE OF THE ISSUER’S REGISTRATION STATEMENT FILED UNDER THE ACT, AS AMENDED, AS SET FORTH IN AN AGREEMENT BETWEEN THE COMPANY AND THE ORIGINAL HOLDER OF THESE SECURITIES, A COPY OF WHICH MAY BE OBTAINED AT THE ISSUER’S PRINCIPAL OFFICE. SUCH LOCK-UP PERIOD IS BINDING ON TRANSFEREES OF THESE SHARES.

SECTION 11. TRANSFERS.

Subject to compliance with applicable federal and state securities laws, this Warrant and all rights hereunder are transferable, in whole or in part, without charge to the holder hereof (except for transfer taxes) upon surrender of this Warrant properly endorsed. Each taker and holder of this Warrant, by taking or holding the same, consents and agrees that this Warrant, when endorsed in blank, shall be deemed negotiable, and that the holder

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hereof, when this Warrant shall have been so endorsed and its transfer recorded on the Company’s books, shall be treated by the Company and all other persons dealing with this Warrant as the absolute owner hereof for any purpose and as the person entitled to exercise the rights represented by this Warrant. The transfer of this Warrant shall be recorded on the books of the Company upon receipt by the Company of a notice of transfer in the form attached hereto as Exhibit III (the “Transfer Notice”), at its principal offices and the payment to the Company of all transfer taxes and other governmental charges imposed on such transfer. Until the Company receives such Transfer Notice, the Company may treat the registered owner hereof as the owner for all purposes.

SECTION 12. MISCELLANEOUS.

(a) Effective Date. The provisions of this Warrant shall be construed and shall be given effect in all respects as if it had been executed and delivered by the Company on the date hereof. This Warrant shall be binding upon any successors or assigns of the Company.

(b) Remedies. In the event of any default hereunder, the non-defaulting party may proceed to protect and enforce its rights either by suit in equity and/or by action at law, including but not limited to an action for damages as a result of any such default, and/or an action for specific performance for any default where such party will not have an adequate remedy at law and where damages will not be readily ascertainable. Each party expressly agrees that it shall not oppose an application by the other party or any other person entitled to the benefit of this Warrant requiring specific performance of any or all provisions hereof or enjoining such party from continuing to commit any such breach of this Warrant.

(c) No Impairment of Rights. The Company will not, by amendment of its Charter or through any other means, avoid or seek to avoid the observance or performance of any of the terms of this Warrant, but will at all times in good faith assist in the carrying out of all such terms and in the taking of all such actions as may be necessary or appropriate in order to protect the rights of the Warrantholder against impairment.

(d) Additional Documents. The Company shall also supply such other documents as the Warrantholder may from time to time reasonably request.

(e) Attorney’s Fees. In any litigation, arbitration or court proceeding between the Company and the Warrantholder relating hereto, the prevailing party shall be entitled to attorneys’ fees and expenses and all costs of proceedings incurred in enforcing this Warrant. For the purposes of this Section 12(e), attorneys’ fees shall include without limitation fees incurred in connection with the following: (i) contempt proceedings; (ii) discovery; (iii) any motion, proceeding or other activity of any kind in connection with an insolvency proceeding; (iv) garnishment, levy, and debtor and third party examinations; and (v) post judgment motions and proceedings of any kind, including without limitation any activity taken to collect or enforce any judgment.

(f) Severability. In the event any one or more of the provisions of this Warrant shall for any reason be held invalid, illegal or unenforceable, the remaining provisions of this Warrant shall be unimpaired, and the invalid, illegal or unenforceable provision shall be replaced by a mutually acceptable valid, legal and enforceable provision, which comes closest to the intention of the parties underlying the invalid, illegal or unenforceable provision.

(g) Notices. Except as otherwise provided herein, any notice, demand, request, consent, approval, declaration, service of process or other communication that is required, contemplated, or permitted under this Warrant or with respect to the subject matter hereof shall be in writing, and shall be deemed to have been validly served, given, delivered, and received upon the earlier of; (i) the first business day after transmission by facsimile or hand delivery or deposit with an overnight express service or overnight mail delivery service; or (ii) the third calendar day after deposit in the United States mails, with proper first class postage prepaid (provided, that any Advance Request shall not be deemed received until Lender’s actual receipt thereof), and shall be addressed to the party to be notified as follows;

If to Warrantholder:

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COMERICA BANK

Attn: Warrant Administrator

500 Woodward Avenue, 32^nd Floor, MC 3379

Detroit, MI 48226

If to the Company:

Horizon Therapeutics, Inc.

533 Bryant Street

Palo Alto, CA 94301

Attention: Barry Golombik

Facsimile:

Telephone:

or to such other address as each party may designate for itself by like notice.

(h) Entire Agreement: Amendments. This Warrant constitutes the entire agreement and understanding of the parties hereto in respect of the subject matter hereof, and supersedes and replaces in its entirety any prior proposals, term sheets, letters, negotiations or other documents or agreements, whether written or oral, with respect to the subject matter hereof (including Holder’s proposal letter dated May 9, 2007). None of the terms of this Warrant may be amended except by an instrument executed by each of the parties hereto.

(i) Headings. The various headings in this Warrant are inserted for convenience only and shall not affect the meaning or interpretation of this Warrant or any provisions hereof.

(j) Advice of Counsel. Each of the parties represents to each other party hereto that it has discussed (or had an opportunity to discuss) with its counsel this Warrant and, specifically, the provisions of Sections 12(n), 12(o), 12(p), 12(q) and 12(r).

(k) No Strict Construction. The parties hereto have participated jointly in the negotiation and drafting of this Warrant. In the event an ambiguity or question of intent or interpretation arises, this Warrant shall be construed as if drafted jointly by the parties hereto and no presumption or burden of proof shall arise favoring or disfavoring any party by virtue of the authorship of any provisions of this Warrant.

(l) No Waiver. No omission or delay by either party at any time to enforce any right or remedy reserved to it, or to require performance of any of the terms, covenants or provisions hereof by the other party at any time designated, shall be a waiver of any such right or remedy to which such party is entitled, nor shall it in any way affect the right of such party to enforce such provisions thereafter.

(m) Survival. All agreements, representations and warranties contained in this Warrant or in any document delivered pursuant hereto shall survive the execution and delivery of this Warrant and the expiration or other termination of this Warrant.

(n) Governing Law. This Warrant has been negotiated and delivered to Warrantholder in the State of California, and shall have been accepted by Warrantholder in the State of California. Delivery of Warrant Stock to Warrantholder by the Company under this Warrant is due in the State of California. This Warrant shall be governed by, and construed and enforced in accordance with, the laws of the State of California, excluding conflict of laws principles that would cause the application of laws of any other jurisdiction.

(o) Consent to Jurisdiction and Venue. All judicial proceedings arising in or under or related to this Warrant may be brought in any state or federal court of competent jurisdiction located in the State of California. By execution and delivery of this Warrant, each parry hereto generally and unconditionally: (a) consents to personal jurisdiction in San Mateo County, State of California; (b) waives any objection as to jurisdiction or venue in San Mateo County, State of California; (c) agrees not to assert any defense based on lack of jurisdiction or venue in the aforesaid courts; and (d) irrevocably agrees to be bound by any judgment rendered thereby in connection with this

9.

Warrant. Service of process on any party hereto in any action arising out of or relating to this Warrant shall be effective if given in accordance with the requirements for notice set forth in Section 12(g), and shall be deemed effective and received as set forth in Section 12(g). Nothing herein shall affect the right to serve process in any other manner permitted by law or shall limit the right of either party to bring proceedings in the courts of any other jurisdiction.

(p) Mutual Waiver of Jury Trial. Because disputes arising in connection with complex financial transactions are most quickly and economically resolved by an experienced and expert person and the parties wish applicable state and federal laws to apply (rather than arbitration rules), the parties desire that their disputes be resolved by a judge applying such applicable laws. EACH OF THE COMPANY AND WARRANTHOLDER SPECIFICALLY WAIVES ANY RIGHT IT MAY HAVE TO TRIAL BY JURY OF ANY CAUSE OF ACTION, CLAIM, CROSS-CLAIM, COUNTERCLAIM, THIRD PARTY CLAIM OR ANY OTHER CLAIM (COLLECTIVELY, “CLAIMS”) ASSERTED BY THE COMPANY AGAINST WARRANTHOLDER OR ITS ASSIGNEE OR BY WARRANTHOLDER OR ITS ASSIGNEE AGAINST THE COMPANY. This waiver extends to all such Claims, including Claims that involve persons other than the Company and Warrantholder; Claims that arise out of or are in any way connected to the relationship between the Company and Warrantholder; and any Claims for damages, breach of contract, specific performance, or any equitable or legal relief of any kind, arising out of this Warrant.

(q) Judicial Reference. if the Mutual Waiver of Jury Trial set forth in Section 12(p) is ineffective or unenforceable, the parties agree that all Claims shall be submitted to a mutually acceptable referee sitting without a jury and resolved pursuant to Code of Civil Procedure Section 638 et seq or, if there is no mutually acceptable referee, then a referee sitting without a jury appointed by the Presiding Judge of the California Superior Court for Santa Clara County. Notwithstanding the foregoing, either party may seek from a court of competent jurisdiction identified in Section 12(o), any prejudgment order, writ or other relief and have such prejudgment order, writ or other relief enforced to the fullest extent permitted by law notwithstanding that all Claims are otherwise subject to resolution by judicial reference.

(r) Counterparts. This Warrant and any amendments, waivers, consents or supplements hereto may be executed in any number of counterparts, and by different parties hereto in separate counterparts, each of which when so delivered shall he deemed an original, but all of which counterparts shall constitute but one and the same instrument.

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10.

IN WITNESS WHEREOF, the parties hereto have caused this Warrant Agreement to be executed by its officers thereunto duly authorized as of the Effective Date.

11.

IN WITNESS WHEREOF, the parties hereto have caused this Warrant Agreement to be executed by its officers thereunto duly authorized as of the Effective Date.

11.

EXHIBIT I

NOTICE OF EXERCISE

EXHIBIT II

ACKNOWLEDGMENT OF EXERCISE

The undersigned [                            ], hereby acknowledge receipt of the “Notice of Exercise” from Comerica Bank, to purchase [    ] shares of the Series [    ] Preferred Stock of [                    ], pursuant to the terms of the Warrant, and further acknowledges that [    ] shares remain subject to purchase under the terms of the Warrant.

EXHIBIT III

TRANSFER NOTICE

(To transfer or assign the foregoing Warrant execute this form and supply required information. Do not use this form to purchase shares.)

FOR VALUE RECEIVED, the foregoing Warrant and all rights evidenced thereby are hereby transferred and assigned to