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 OF SECURITIES 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 * Zhang Jack Y.   2. Issuer Name and Ticker or Trading Symbol Amphastar Pharmaceuticals, Inc. [AMPH] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) __X__ Director __X__ 10% Owner __X__ Officer (give title below) _____ Other (specify below) CEO & Chief Scientific Officer (Last) (First) (Middle) C/O AMPHASTAR PHARMACEUTICALS, INC., 11570 6TH STREET 3. Date of Earliest Transaction (Month/Day/Year) 05/15/2018 (Street) RANCHO CUCAMONGA, CA 91730 4. If Amendment, Date Original Filed(Month/Day/Year) 6. Individual or Joint/Group Filing(Check Applicable Line) ___ Form filed by One Reporting Person _X_ 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 (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 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 05/15/2018   P   25,000 A $ 16.0788 (1) 2,065,619 D   Common Stock 05/16/2018   P   15,000 A $ 16.0569 (2) 2,080,619 D   Common Stock               1,346,129 I See footnote (3) Common Stock               7,461,594 I See footnote (4) Common Stock               5,000 I See footnote (5) Common Stock               200,000 I See footnote (6)

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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 (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

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 (Month/Day/Year)

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

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
Zhang Jack Y. C/O AMPHASTAR PHARMACEUTICALS, INC. 11570 6TH STREET RANCHO CUCAMONGA, CA 91730	X	X	CEO & Chief Scientific Officer
Luo Mary Z. C/O AMPHASTAR PHARMACEUTICALS, INC. 11570 6TH STREET RANCHO CUCAMONGA, CA 91730	X	X	COO,Chief Scientist & Chairman

Signatures

/s/ Eva H. Wen, by power of attorney for Jack Y. Zhang		05/17/2018
**Signature of Reporting Person		Date
/s/ Eva H. Wen, by power of attorney for Mary Z. Luo		05/17/2018
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $15.762 to $16.50 inclusive. The reporting persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the ranges set forth in footnotes (1) and (2) to this Form 4.
(2)	The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $15.997 to $16.063, inclusive.
(3)	The securities are held of record by Mary Z. Luo. The reporting persons are husband and wife.
(4)	The shares are held of record by APCL, of which the reporting persons and The Bill Luobei Zhang 2004 Irrevocable Trust (the "BLZ Trust") are the sole owners.
(5)	The shares are held of record in an account for the benefit of the reporting persons' son. The reporting persons disclaim beneficial ownership of these shares, and the inclusion of these shares in this report should not be deemed an admission of beneficial ownership of any such shares for purposes of Section 16, or for any other purpose.
(6)	The shares are held of record by the BLZ Trust. The reporting persons disclaim beneficial ownership of these shares, and the inclusion of these shares in this report should not be deemed an admission of beneficial ownership of any such shares for purposes of Section 16, or for any other purpose.

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