Exhibit 32.2

Certification of Chief Financial Officer pursuant to 18 U.S.C. Section 1350, as adopted

pursuant to Section 906 of the Sarbanes-Oxley Act of 2002

The undersigned officer of Amphastar Pharmaceuticals, Inc. (the “Company”), hereby certifies, to the best of such officer’s knowledge, that:

(i) the Quarterly Report on Form 10-Q of the Company for the quarter ended March 31, 2018 (the “Report”) fully complies with the requirements of Section 13(a) or Section 15(d) of the Securities Exchange Act of 1934 and

(ii) the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company at the dates and for the periods indicated.

Date: May 10, 2018	By:	/s/ WILLIAM J. PETERS
		William J. Peters
		Chief Financial Officer
		(Principal Financial and Accounting Officer)

The foregoing certification is being furnished solely to accompany the Report pursuant to 18 U.S.C. §1350, and is not being filed for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, and is not to be incorporated by reference into any filing of the Company, whether made before or after the date hereof, regardless of any general incorporation language in such filing.