X0306 4 2019-09-05 0 0001297184 Amphastar Pharmaceuticals, Inc. AMPH 0001743927 Liawatidewi Yakob C/O AMPHASTAR PHARMACEUTICALS, INC. 11570 6TH STREET RANCHO CUCAMONGA CA 91730 0 1 0 0 SVP Corp Admin Center Common Stock 2019-09-05 4 S 0 1515 21.2433 D 4854 I See footnote Common Stock 2019-09-06 4 S 0 2395 21.9018 D 2459 I See footnote Common Stock 36670 D The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $21.24 to $21.27, inclusive. The reporting person undertakes 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 sold at each separate price within the ranges set forth in footnotes (1) and (3) to this Form 4. The reported shares are held of record by the Yakob and Sunmoon Trust dated July 25, 2013 for which the reporting person serves as a trustee. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $21.90 to $21.92, inclusive. /s/ Eva Wen, by power of attorney 2019-09-09