Amphastar CFO reports RSU tax share withholding

Rhea-AI Filing Summary

Amphastar Pharmaceuticals CFO William J. Peters reported a routine tax-related share disposition. On the vesting of restricted stock units, 1,973 shares of common stock were withheld at $18.18 per share to satisfy his tax liability, rather than sold on the open market.

After this withholding, Peters directly holds 175,063 shares of Amphastar common stock. This filing reflects a compensation-driven, non-discretionary tax-withholding event, not an open-market purchase or sale decision.

Insider Trade Summary

Net Seller: 1,973 shares

Net Sell 1 txn

Insider PETERS WILLIAM J

Role CFO, EVP & TREASURER

Type	Security	Shares	Price	Value
Exercise Price or Tax Liability	Common Stock	1,973	$18.18	$36K

Holdings After Transaction: Common Stock — 175,063 shares (Direct)

Footnotes (1)

1. F1. The reported shares were withheld to satisfy the reporting person's tax liability in connection with the vesting of restricted stock units, or RSUs.

FAQ

What insider transaction did Amphastar (AMPH) report for CFO William J. Peters?

Amphastar’s CFO William J. Peters reported shares withheld for taxes, not an open-market trade. 1,973 common shares were retained by the company to cover tax obligations when his restricted stock units vested.

How many Amphastar (AMPH) shares were withheld for CFO Peters’ tax obligations?

A total of 1,973 Amphastar common shares were withheld to satisfy CFO William J. Peters’ tax liability upon RSU vesting. The shares were valued at $18.18 each for this tax-withholding transaction.

Was the Amphastar (AMPH) CFO’s Form 4 transaction a stock sale?

The CFO’s Form 4 transaction was a tax-withholding disposition, not an open-market sale. Shares were withheld by Amphastar to pay taxes when restricted stock units vested, a standard compensation-related event.

How many Amphastar (AMPH) shares does CFO William J. Peters hold after this filing?

Following the tax-withholding event, CFO William J. Peters directly holds 175,063 Amphastar common shares. This remaining position shows he continues to maintain a substantial equity stake after covering his RSU-related tax obligations.

What was the price used for the Amphastar (AMPH) CFO tax-withholding shares?

The 1,973 Amphastar shares withheld for CFO William J. Peters’ taxes were valued at $18.18 per share. This price is used solely to determine the tax-withholding amount tied to his restricted stock unit vesting.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 03/17/2026 - 06:14 PM Learn about SEC filing dates

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

PETERS WILLIAM J

(Last) (First) (Middle)

C/O AMPHASTAR PHARMACEUTICALS, INC.

11570 6TH STREET

(Street)

RANCHO CUCAMONGA CA 91730

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Amphastar Pharmaceuticals, Inc. [ AMPH ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	CFO, EVP & TREASURER

3. Date of Earliest Transaction (Month/Day/Year)
03/15/2026

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	03/15/2026		F		1,973(1)	D	$18.18	175,063	D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

1. The reported shares were withheld to satisfy the reporting person's tax liability in connection with the vesting of restricted stock units, or RSUs.

	/s/ William J. Peters	03/17/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.