Entry into Material Definitive Agreement and Amendment of a Material Definitive Agreement.

Supply Agreement.

On March 3, 2026, (the "Effective Date"), Amphastar Nanjing Pharmaceuticals, Inc. ("ANP"), the Chinese subsidiary of Amphastar Pharmaceuticals, Inc. ("Amphastar" or, the "Company"), entered into a supply agreement (the "Supply Agreement") with Nanjing Letop Biotechnology Co., Ltd. ("Letop"). Pursuant to the Supply Agreement, Letop will manufacture and deliver chemical intermediates ("Intermediates") for ANP according to the requirements of the purchase orders confirmed by Letop (collectively, the "Transaction"). ANP is entitled to decide the quantity of the Intermediates that it purchases from Letop at its own discretion, and ANP has no obligation to purchase any minimum quantity of the Intermediates from Letop. ANP will retain ownership of all confidential information ANP shares with Letop during the term of this Supply Agreement. Each of ANP and Letop have made customary representations, warranties and covenants in the Supply Agreement. This Supply Agreement will remain in full force and effect for a period of five (5) years from the Effective Date. Payments under the Supply Agreement will be made in Chinese yuan. The Company does not consider this Supply Agreement to be material to its financial condition or results of operations.

As previously disclosed in the Company's Annual Report on Form 10-K for the fiscal year ended December 31, 2025, as filed with the Securities Exchange Commission ("SEC") on February 26, 2026, Henry Zhang is an immediate family member of Dr. Jack Zhang, Chief Executive Officer, President, and Director of the Company, Dr. Mary Luo, Chairman, Chief Operating Officer, and Director of the Company. Henry Zhang beneficially owns a majority of the equity interest in Letop, and the Agreement with Letop represents a related party transaction. Accordingly, the members of the Audit Committee of the Board of Directors of the Company evaluated and approved the Transaction and entry into the Agreement following their review of applicable considerations.

The foregoing is a brief description of the material terms of the Supply Agreement, does not purport to be a complete description of the rights and obligations of the parties thereunder, and is qualified in its entirety by reference to the copies of the Supply Agreement, a copy of which is filed as Exhibit 10.1 hereto and incorporated herein by reference.