X0306 4 2021-02-10 0 0001297184 Amphastar Pharmaceuticals, Inc. AMPH 0001611157 Zhang Jack Y. C/O AMPHASTAR PHARMACEUTICALS, INC. 11570 6TH STREET RANCHO CUCAMONGA CA 91730 1 1 1 0 CEO & Chief Scientific Officer 0001611156 Luo Mary Z. C/O AMPHASTAR PHARMACEUTICALS, INC. 11570 6TH STREET RANCHO CUCAMONGA CA 91730 1 1 1 0 COO, Chief Scientist & Chairma 0001611158 Applied Physics & Chemistry Laboratories, Inc. C/O AMPHASTAR PHARMACEUTICALS, INC. 11570 6TH STREET RANCHO CUCAMONGA CA 91730 0 0 1 0 Common Stock 2021-02-10 4 S 0 15747 18.7556 D 6891246 I See footnote Common Stock 2021-02-11 4 S 0 19823 19.0629 D 6871423 I See footnote Common Stock 2021-02-12 4 S 0 13277 18.9442 D 6858146 I See footnote Common Stock 2246988 D Common Stock 1449961 I See footnote Common Stock 5000 I See footnote The sales reported in this Form 4 was effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on June 12, 2020. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $18.48 to $18.97, 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 (2), (4) and (5). The shares are held of record by Applied Physics & Chemistry Laboratories, Inc., of which the reporting persons and The Bill Luobei Zhang 2004 Irrevocable Trust (the "BLZ Trust") are the sole owners. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $18.805 to $19.19, inclusive. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $18.85 to $19.18, inclusive. The securities are held of record by Mary Z. Luo. The reporting persons are husband and wife. 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. /s/ William J. Peters, by power of attorney for Jack Y. Zhang 2021-02-12 /s/ William J. Peters, by power of attorney for Mary Z. Luo 2021-02-12 /s/ William J. Peters, by power of attorney for Jack Y. Zhang, principal and owner of Applied Physics & Chemistry Laboratories, Inc. 2021-02-12