X0508 4 2025-12-17 0001297184 Amphastar Pharmaceuticals, Inc. AMPH 0001645326 Zhou Rong C/O AMPHASTAR PHARMACEUTICALS, INC. 11570 6TH STREET RANCHO CUCAMONGA CA 91730 false true false false SENIOR EVP, PRODUCTION CENTER 0 Common Stock 2025-12-17 4 M 0 9787 11.33 A 147830 D Common Stock 2025-12-17 4 S 0 9787 26.1959 D 138043 D Common Stock 99668 I See footnote Common Stock 5000 I See footnote Employee Stock Option (right to buy) 11.33 2025-12-17 4 M 0 9787 0 D 2026-03-17 Common Stock 9787 0 D Includes 545 shares acquired on May 31, 2025 and one share acquired on November 30, 2025 under the Issuer's 2014 Employee Stock Purchase Plan. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $25.97 to $26.50, 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. The shares are held of record by the Zhou Family Trust for which the reporting person serves as a trustee. The shares are held of record by the reporting person's spouse. Shares subject to the option are fully vested and immediately exercisable. /s/ Eva Wen, by power of attorney 2025-12-18