FIRST AMENDMENT TO PATENT ASSIGNMENT AGREEMENT

Exhibit 10.28

CONFIDENTIAL TREATMENT

FIRST AMENDMENT TO PATENT ASSIGNMENT AGREEMENT

This first amendment (the “Amendment”) effective 31 December 2010 is made to the patent assignment dated the 23^rd day of February 2009 (the “Assignment Agreement”) between Omeros Corporation, a Washington corporation having a principal place of business at 1420 Fifth Avenue, Suite 2600, Seattle WA 98101 USA (“Omeros”) and Roberto Ciccocioppo, Ph.D., having a residence at Vicolo San Silvestro n. 25, Camerino, 62032 IT (“Dr. Ciccocioppo”).

WHEREAS Dr. Ciccocioppo previously assigned all rights, in consideration for Omeros undertaking certain future milestone and royalty obligations in accordance with the terms of the Assignment Agreement to certain technology invented by Dr. Ciccocioppo related to new uses of peroxisome proliferator-activated receptor gamma (“PPARg”) agonists for the prevention and treatment and addictions and compositions including PPARg agonists, alone or in combination with other agents, including, without limitation, compositions regulated by the U.S. Food and Drug Administration and corresponding foreign regulatory agents that contain one or more PPARg agonist(s) as active pharmaceutical ingredient(s) (the “PPARg Pharmaceuticals”); and

WHEREAS Dr. Ciccocioppo has conceived a related concept directed to the use of dietary supplement (i.e., nutraceutical) compositions comprising fatty acids that increase the activity of the PPARg pathway for use in the treatment and prevention of disorders affected by PPARg activation, including, without limitation, alcoholism, addiction and compulsive disorders, as well as nutraceutical compositions containing fatty acids that activate PPARg that are not regulated by the U.S. Food and Drug Administration and corresponding foreign regulatory agents (altogether the “PPARg Nutraceutical Technology” and with respect to compositions the “PPARg Nutraceuticals”);

WHEREAS Omeros and Dr. Ciccocioppo wish to confirm the assignment to Omeros of all rights related to the PPARg Nutraceutical Technology and the PPARg Nutraceuticals in accordance with and as part of the Assignment Agreement and wish to further compensate Dr. Ciccocioppo for these advances;

NOW THEREFORE, in consideration for the mutual covenants and obligations set forth herein as well as other good and valuable consideration, the parties hereby agree as follows. All initial capitalized terms used in this Amendment without definition or redefinition shall have the same definition as set forth in the Assignment Agreement:

† DESIGNATES PORTIONS OF THIS DOCUMENT THAT HAVE BEEN OMITTED PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT FILED SEPARATELY WITH THE COMMISSION

Section 4.1 and the accompanying table of the Assignment Agreement shall be replaced with the following amended Section 4.1 and accompanying table.

† DESIGNATES PORTIONS OF THIS DOCUMENT THAT HAVE BEEN OMITTED PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT FILED SEPARATELY WITH THE COMMISSION

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† DESIGNATES PORTIONS OF THIS DOCUMENT THAT HAVE BEEN OMITTED PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT FILED SEPARATELY WITH THE COMMISSION

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IN WITNESS WHEREOF, Omeros and Dr. Ciccocioppo have each acknowledged and accepted this Amendment by signing or causing it to have been signed by a duly authorized official.

The Università di Camerino, employer of Roberto Ciccocioppo, through the undersigned official thereof, hereby consents to all of the transactions provided for in the above Amendment.

† DESIGNATES PORTIONS OF THIS DOCUMENT THAT HAVE BEEN OMITTED PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT FILED SEPARATELY WITH THE COMMISSION

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