<SEC-DOCUMENT>0001297184-24-000029.txt : 20240419
<SEC-HEADER>0001297184-24-000029.hdr.sgml : 20240419
<ACCEPTANCE-DATETIME>20240419162129
ACCESSION NUMBER:		0001297184-24-000029
CONFORMED SUBMISSION TYPE:	DEFA14A
PUBLIC DOCUMENT COUNT:		1
FILED AS OF DATE:		20240419
DATE AS OF CHANGE:		20240419

FILER:

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Amphastar Pharmaceuticals, Inc.
		CENTRAL INDEX KEY:			0001297184
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		ORGANIZATION NAME:           	03 Life Sciences
		IRS NUMBER:				330702205
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		DEFA14A
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-36509
		FILM NUMBER:		24858050

	BUSINESS ADDRESS:	
		STREET 1:		11570 SIXTH STREET
		CITY:			RANCHO CUCAMONGA
		STATE:			CA
		ZIP:			91730
		BUSINESS PHONE:		909-980-9484

	MAIL ADDRESS:	
		STREET 1:		11570 SIXTH STREET
		CITY:			RANCHO CUCAMONGA
		STATE:			CA
		ZIP:			91730
</SEC-HEADER>
<DOCUMENT>
<TYPE>DEFA14A
<SEQUENCE>1
<FILENAME>amph-20240419xdefa14a.htm
<DESCRIPTION>DEFA14A
<TEXT>
<!--Enhanced HTML document created with Toppan Merrill Bridge  10.5.122.0--><!--Created on: 4/19/2024 04:35:34 PM (UTC)--><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta charset="UTF-8"><title></title></head><body><div style="margin-top:30pt;"></div><div style="max-width:100%;padding-left:10.35%;padding-right:10.35%;position:relative;"><div style="clear:both;max-width:100%;position:relative;"><div style="padding-top:1.0px;border-top:3.0pt solid #000000;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;font-weight:bold;line-height:1.12;padding-top:6pt;text-align:center;text-indent:0pt;border-top:1.0pt solid #000000;margin:0pt;"><b style="font-size:14pt;font-weight:bold;">UNITED STATES</b></p></div><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;font-weight:bold;line-height:1.12;text-align:center;text-indent:0pt;margin:0pt;"><b style="font-size:14pt;font-weight:bold;">SECURITIES AND EXCHANGE COMMISSION</b></p><p style="font-family:'Times New Roman','Times','serif';font-size:10pt;font-weight:bold;line-height:1.12;text-align:center;text-indent:0pt;margin:0pt;">Washington, D.C. 20549</p><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;font-weight:bold;line-height:1.12;text-align:center;text-indent:0pt;margin:6pt 0pt 0pt 0pt;"><b style="font-size:14pt;font-weight:bold;">SCHEDULE&#160;14A</b></p><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;font-weight:bold;line-height:1.12;text-align:center;text-indent:0pt;margin:6pt 0pt 12pt 0pt;">PROXY STATEMENT PURSUANT TO SECTION 14(a) OF THE<br>SECURITIES EXCHANGE ACT OF 1934 (Amendment No. )</p><div><table style="border-collapse:collapse;font-size:16pt;height:max-content;margin-left:auto;margin-right:auto;padding-left:3.6pt;padding-right:3.6pt;table-layout:auto;width:100%;" align="center"><tr style="height:1pt;"><td style="vertical-align:top;width:3.49%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><div style="height:1pt;overflow:hidden;overflow-wrap:break-word;position:relative;"><div style="position:absolute;top:0pt;width:100%;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;text-indent:36pt;margin:12pt 0pt 0pt 0pt;"><font style="font-size:1pt;visibility:hidden;">&#8203;</font></p></div></div></td><td style="vertical-align:top;width:4.84%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><div style="height:1pt;overflow:hidden;overflow-wrap:break-word;position:relative;"><div style="position:absolute;top:0pt;width:100%;"></div></div></td><td style="vertical-align:top;width:91.66%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><div style="height:1pt;overflow:hidden;overflow-wrap:break-word;position:relative;"><div style="position:absolute;top:0pt;width:100%;"></div></div></td></tr><tr><td colspan="3" style="vertical-align:top;width:100%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:10pt;line-height:12pt;padding-left:10pt;text-indent:-10pt;margin:3pt 0pt 0pt 0pt;"><font style="font-size:11pt;white-space:pre-wrap;">Filed by the Registrant  </font><font style="font-family:'Times New Roman';">&#8999;</font></p></td></tr><tr><td colspan="3" style="vertical-align:top;width:100%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;padding-left:10.1pt;text-indent:-10.1pt;margin:3pt 0pt 0pt 0pt;"><font style="white-space:pre-wrap;">Filed by a Party other than the Registrant  </font><font style="font-family:'Times New Roman';">&#9723;</font></p></td></tr><tr><td colspan="3" style="vertical-align:top;width:100%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;padding-left:10.1pt;text-indent:-10.1pt;margin:3pt 0pt 0pt 0pt;"><font style="font-size:12pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;padding-left:10.1pt;text-indent:-10.1pt;margin:3pt 0pt 0pt 0pt;">Check the appropriate box:</p></td></tr><tr><td style="vertical-align:top;width:3.49%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;padding-left:10pt;text-indent:-10pt;margin:3pt 0pt 0pt 0pt;"><font style="font-family:'Times New Roman';">&#9723;</font></p></td><td colspan="2" style="vertical-align:top;width:96.5%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;text-indent:0pt;margin:3pt 0pt 0pt 0pt;">Preliminary Proxy Statement</p></td></tr><tr><td style="vertical-align:top;width:3.49%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;padding-left:10pt;text-indent:-10pt;margin:3pt 0pt 0pt 0pt;"><font style="font-family:'Times New Roman';">&#9723;</font></p></td><td colspan="2" style="vertical-align:top;width:96.5%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;text-indent:0pt;margin:3pt 0pt 0pt 0pt;"><b style="font-weight:bold;">Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))</b></p></td></tr><tr><td style="vertical-align:top;width:3.49%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;padding-left:10pt;text-indent:-10pt;margin:3pt 0pt 0pt 0pt;"><font style="font-family:'Times New Roman';">&#9723;</font></p></td><td colspan="2" style="vertical-align:top;width:96.5%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;text-indent:0pt;margin:3pt 0pt 0pt 0pt;">Definitive Proxy Statement</p></td></tr><tr><td style="vertical-align:top;width:3.49%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;padding-left:10pt;text-indent:-10pt;margin:3pt 0pt 0pt 0pt;"><font style="font-family:'Times New Roman';">&#8999;</font></p></td><td colspan="2" style="vertical-align:top;width:96.5%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;text-indent:0pt;margin:3pt 0pt 0pt 0pt;">Definitive Additional Materials</p></td></tr><tr><td style="vertical-align:top;width:3.49%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;padding-left:10pt;text-indent:-10pt;margin:3pt 0pt 0pt 0pt;"><font style="font-family:'Times New Roman';">&#9723;</font></p></td><td colspan="2" style="vertical-align:top;width:96.5%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;text-indent:0pt;margin:3pt 0pt 0pt 0pt;">Soliciting Material Pursuant to &#167;240.14a-12</p></td></tr><tr><td colspan="3" style="vertical-align:top;width:100%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;text-align:center;text-indent:0pt;margin:3pt 0pt 0pt 0pt;"><font style="font-size:12pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p></td></tr><tr><td colspan="3" style="vertical-align:top;width:100%;border-bottom:1px solid #000000;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;text-align:center;text-indent:0pt;margin:3pt 0pt 0pt 0pt;"><b style="font-size:14pt;font-weight:bold;">AMPHASTAR PHARMACEUTICALS, INC.</b></p></td></tr><tr><td colspan="3" style="vertical-align:top;width:100%;border-top:1px solid #000000;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:10pt;line-height:12pt;text-align:center;text-indent:0pt;margin:3pt 0pt 0pt 0pt;"><b style="font-weight:bold;">(Name of Registrant as Specified In Its Charter)</b></p></td></tr><tr><td colspan="3" style="vertical-align:top;width:100%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:10pt;line-height:12pt;text-align:center;text-indent:0pt;margin:3pt 0pt 0pt 0pt;"><b style="font-weight:bold;">(Name of Person(s) Filing Proxy Statement, if other than the Registrant)</b></p></td></tr><tr><td colspan="3" style="vertical-align:top;width:100%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;padding-left:10pt;text-indent:-10pt;margin:3pt 0pt 0pt 0pt;"><font style="font-size:12pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p></td></tr><tr><td colspan="3" style="vertical-align:top;width:100%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;padding-left:10pt;text-indent:-10pt;margin:3pt 0pt 0pt 0pt;">Payment of Filing Fee (Check the appropriate box):</p></td></tr><tr><td style="vertical-align:top;width:3.49%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;padding-left:10pt;text-indent:-10pt;margin:3pt 0pt 0pt 0pt;"><font style="font-family:'Times New Roman';">&#8999;</font></p></td><td colspan="2" style="vertical-align:top;width:96.5%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;text-indent:0pt;margin:3pt 0pt 0pt 0pt;">No fee required.</p></td></tr><tr><td style="vertical-align:top;width:3.49%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;padding-left:10pt;text-indent:-10pt;margin:3pt 0pt 0pt 0pt;"><font style="font-family:'Times New Roman';">&#9723;</font></p></td><td colspan="2" style="vertical-align:top;width:96.5%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;text-indent:0pt;margin:3pt 0pt 0pt 0pt;">Fee paid previously with preliminary materials.</p></td></tr><tr><td style="vertical-align:top;width:3.49%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;padding-left:10pt;text-indent:-10pt;margin:3pt 0pt 0pt 0pt;"><font style="font-family:'Times New Roman';">&#9723;</font></p></td><td colspan="2" style="vertical-align:top;width:96.5%;margin:0pt;padding:0pt 3.59pt 0pt 3.59pt;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;line-height:12pt;text-indent:0pt;margin:3pt 0pt 0pt 0pt;">Fee computed on table below per Exchange Act Rules 14a-6(i)(1) and&#160;0-11.</p></td></tr></table></div><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;text-indent:0pt;margin:0pt;"><font style="font-size:1pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="border-bottom-style:none;font-family:'Times New Roman','Times','serif';font-size:11pt;padding-top:0pt;text-indent:0pt;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p></div></div><hr style="background-color:#000000;clear:both;color:#000000;height:2pt;line-height:0;margin-bottom:30pt;margin-left:10.35%;margin-right:10.35%;margin-top:30pt;page-break-after:always;width:79.3%;border-width:0;"><div style="max-width:100%;padding-left:10.35%;padding-right:10.35%;position:relative;"><div style="margin-top:7.2pt;width:100%;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;text-indent:0pt;margin:0pt 0pt 30pt 0pt;"><a href="#Toc"></a><font style="color:#0563c1;font-size:10pt;visibility:hidden;">&#8203;</font></p></div><div style="clear:both;max-width:100%;position:relative;"><div style="padding-bottom:1.0px;border-bottom:3.0pt solid #000000;"><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;padding-bottom:1pt;padding-top:0pt;text-indent:0pt;border-bottom:1.0pt solid #000000;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p></div><p style="font-family:'Times New Roman','Times','serif';font-size:11pt;text-indent:0pt;background:#ffffff;margin:0pt;"><font style="font-size:10pt;margin-top:12pt;visibility:hidden;">&#8203;</font></p><p style="font-family:'Times New Roman','Times','serif';font-size:10pt;text-align:center;text-indent:36pt;background:#ffffff;margin:0pt;"><b style="font-weight:bold;text-transform:uppercase;">SUPPLEMENT TO PROXY STATEMENT DATED APRIL 12, 2024,</b></p><p style="font-family:'Times New Roman','Times','serif';font-size:10pt;text-align:center;text-indent:36pt;background:#ffffff;margin:0pt;"><b style="font-weight:bold;text-transform:uppercase;">FOR THE ANNUAL MEETING OF STOCKHOLDERS</b></p><p style="font-family:'Times New Roman','Times','serif';font-size:10pt;text-align:center;text-indent:36pt;background:#ffffff;margin:0pt;"><b style="font-weight:bold;text-transform:uppercase;">TO BE HELD ON JUNE 3, 2024</b></p><p style="font-family:'Times New Roman','Times','serif';font-size:10pt;text-indent:36pt;background:#ffffff;margin:0pt;">&#160;</p><p style="font-family:'Times New Roman','Times','serif';font-size:10pt;text-indent:0pt;background:#ffffff;margin:0pt;">This supplement (this &#8220;Supplement&#8221;), dated April 19, 2024, supplements and amends the definitive proxy statement (the &#8220;Proxy Statement&#8221;) filed by Amphastar Pharmaceuticals, Inc. (the &#8220;Company&#8221;) with the Securities and Exchange Commission (the &#8220;SEC&#8221;) on April 12, 2024 for the 2024 Annual Meeting of Stockholders to be held on June 3, 2024 (the &#8220;Annual Meeting&#8221;). This Supplement is being filed to correct an inadvertent error and to clarify the voting standard for Proposal 4 &#8211; <i style="font-style:italic;">Approval of the Amendment and Restatement of Our 2015 Equity Incentive Plan </i>(&#8220;Proposal 4&#8221;)<i style="font-style:italic;">.</i></p><p style="font-family:'Times New Roman','Times','serif';font-size:10pt;text-indent:0pt;background:#ffffff;margin:0pt;">&#160;</p><p style="font-family:'Times New Roman','Times','serif';font-size:10pt;text-indent:0pt;background:#ffffff;margin:0pt;">While the voting standard for Proposal 4 was properly stated on page 3 of the Proxy Statement, due to an inadvertent error on page 36 of the Proxy Statement, the voting standard for Proposal 4 was not set forth properly<i style="font-style:italic;">.</i> This Supplement hereby amends and replaces the language that follows the heading &#8220;Vote Required and Board of Directors Recommendation&#8221; on page 36 of the Proxy Statement with the following language, which aligns with the prior disclosure stated on page 3 of the Proxy Statement:</p><p style="font-family:'Times New Roman','Times','serif';font-size:10pt;text-indent:0pt;background:#ffffff;margin:0pt;">&#160;</p><p style="font-family:'Times New Roman','Times','serif';font-size:10pt;text-indent:0pt;background:#ffffff;margin:0pt 0pt 0pt 36pt;">The Restatement must be approved by the affirmative vote of a majority of the voting power of the shares present or represented by proxy at the Annual Meeting at which a quorum is present and entitled to vote thereon. Abstentions will have the effect of a vote AGAINST the proposal and broker non-votes will have no effect. &#160;</p><p style="font-family:'Times New Roman','Times','serif';font-size:10pt;text-indent:0pt;background:#ffffff;margin:0pt;">&#160;</p><p style="font-family:'Times New Roman','Times','serif';font-size:10pt;text-indent:0pt;background:#ffffff;margin:0pt;">Except as specifically supplemented by the information contained herein, this Supplement does not revise or update any of the other information set forth in the Proxy Statement. This Supplement does not provide all of the information that is important to your voting decisions at the Annual Meeting, and the Proxy Statement contains other important additional information. This Supplement should be read in conjunction with the Proxy Statement.</p><p style="font-family:'Times New Roman','Times','serif';font-size:10pt;text-indent:0pt;background:#ffffff;margin:0pt;">&#160;</p><p style="font-family:'Times New Roman','Times','serif';font-size:10pt;text-indent:0pt;background:#ffffff;margin:0pt;">If you have already returned your proxy or voting instruction card or provided voting instructions, you do not need to take any action unless you wish to change your vote. If you have submitted a proxy and wish to change your vote, you may revoke your proxy and change your vote by following the instructions on page 4 of the Proxy Statement in the section titled &#8220;Questions and Answers about the Proxy Materials and Our Annual Meeting.&#8221; This Supplement does not change the proposals to be acted upon at the Annual Meeting, which are described in the Proxy Statement.</p></div></div><hr style="background-color:#000000;clear:both;color:#000000;height:2pt;line-height:0;margin-left:10.35%;margin-right:10.35%;margin-top:30pt;page-break-after:avoid;width:79.3%;border-width:0;"></body></html>
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