Sec Form 4 Filing - Chang Michael N @ OPTIMER PHARMACEUTICALS INC - 2013-04-03

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Chang Michael N 2. Issuer Name and Ticker or Trading Symbol OPTIMER PHARMACEUTICALS INC [ OPTR] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O OPTIMER PHARMACEUTICALS, INC., 101 HUDSON STREET 3. Date of Earliest Transaction (MM/DD/YY) 04/03/2013 (Street) JERSEY CITY, NJ07302 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common stock 04/03/2013 M 145,312 A $ 12.34 628,568 D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Stock option (right to buy) $ 12.34 04/03/2013 M 42,187 ( 1 ) 04/13/2013 Common stock 42,187 $ 0 0 D Stock option (right to buy) $ 12.34 04/03/2013 M 103,125 ( 2 ) 04/13/2013 Common stock 103,125 $ 0 0 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Chang Michael N C/O OPTIMER PHARMACEUTICALS, INC. 101 HUDSON STREET JERSEY CITY, NJ07302 X Signatures Meredith Schaum, attorney-in-fact 04/05/2013 Signature of Reporting Person Date

Explanation of Responses:

( 1 )On May 5, 2010, the reporting person was granted an option to purchase 50,000 shares of common stock, subject to the satisfaction of certain performance criteria. The performance criteria were met on Augut 18, 2010, at which time the option vested as to 12,500 shares. Thereafter, the remaining shares subject to the option were scheduled to vest and become excercisable in 24 equal monthly installments subject to the reporting person continuing to serve as a consultant. At the time the reporting person's consulting agreement was terminated in April 2012, the option (i) had vested as to an additional 29,687 shares and (ii) was cancelled as to the remaining 7,813 shares. ( 2 )On May 5, 2010, the reporting person was granted an option to purchase 150,000 shares of common stock, subject to the satisfaction of certain performance criteria. The performance criteria were met on January 21, 2011, at which time the option vested as to 37,500 shares. Thereafter, the remaining shares subject to the option were scheduled to vest and become excercisable in 24 equal monthly installments subject to the reporting person continuing to serve as a consultant. At the time the reporting person's consulting agreement was terminated in April 2012, the option (i) had vested as to an additional 65,625 shares and (ii) was cancelled as to the remaining 46,875 shares.

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* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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