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WARNING LETTER

AHC Products, Inc. MARCS-CMS 728604 —

Delivery Method:
VIA Electronic Mail
Product:
Animal & Veterinary
Drugs
Recipient:
Recipient Name
Mr. Michael Wolf
Recipient Title
Compliance Manager and Pharmacist in Charge
AHC Products, Inc.

301 W Broadway St
Winchester, KY 40391-1915
United States

Issuing Office:
Center for Veterinary Medicine

United States

June 12, 2026

CMS Case: 728604

WARNING LETTER

Dear Mr. Wolf:

The United States Food and Drug Administration (FDA) inspected your drug manufacturing facility, AHC Products, Inc., located at 301 W Broadway St, Winchester, KY from October 20 to 23, 2025.

This warning letter summarizes significant violations of FDA’s Current Good Manufacturing Practice (CGMP) regulations for finished pharmaceuticals. See Title 21, Code of Federal Regulations (CFR), parts 210 and 211 (21 CFR parts 210 and 211).

Because your methods, facilities, or controls for manufacturing, processing, packing, or holding do not conform to CGMP, your drug products are adulterated within the meaning of section 501(a)(2)(B) of the Federal Food, Drug, and Cosmetic Act (FD&C Act) [21 U.S.C. § 351(a)(2)(B)].

In addition, this letter concerns your firm’s marketing of several unapproved new animal drugs in violation of the Federal Food Drug and Cosmetic Act (FD&C Act). The specific products include (b)(4), AniPrin P, and Rot-B-Gone.

Current Good Manufacturing Practice Violations

We reviewed your November 13, 2025, response to our Form FDA 483 in detail. We have not received any other correspondence from you regarding the inspection.

Our review of the evidence gathered during the inspection and your response revealed significant violations, including the following.

1. Your firm failed to have, for each batch of drug product, appropriate laboratory determination of satisfactory conformance to final specifications for the drug product, including the identity and strength of each active ingredient, prior to release (21 CFR 211.165(a)).

Your firm manufactures drug products, including (b)(4) wound dressing and Animed AniPrin liquid and powder aspirin products (AniPrin LQ and AniPrin P). Your firm failed to ensure that testing and release of drug products for distribution included appropriate laboratory determination of satisfactory conformance to final specifications prior to release. For example, your firm released (b)(4) lots of (b)(4) without conducting any finished product laboratory testing. Your firm's product release decisions for these lots were based solely on visual assessment of (b)(4) properties. Additionally, your firm listed test results for microbiological hazards and heavy metal content on Certificates of Analysis (COAs) for all manufactured lots of AniPrin F, AniPrin LQ, AniPrin LQ with Caffeine, and AniPrin P without performing the corresponding analytical testing on the finished product batches.

In your response, you stated that for (b)(4), the methodology utilized for product release was color comparison to the original (b)(4) product, and you referenced a scientific publication suggesting that (b)(4) concentration can be reliably estimated by color comparison. You indicated that as part of your investigation, you are investigating a (b)(4) methodology and have preliminarily confirmed through ICP-MS testing that the finished product was approximately (b)(4)% of the (b)(4) raw material. You stated that you are in contact with laboratories to conduct USP testing of the raw material and then validation of methodologies to determine conformance of the finished product to final specifications prior to release.

Regarding the AniPrin products, you stated that the heavy metal specifications and microbiological specifications listed on your COAs are controlled using incoming raw material specifications with random verification. You indicated that COAs for aspirin products will be revised to remove these specifications, and COAs for other products will be modified to clarify that these specifications are controlled by incoming specifications with random verification.

Your response is inadequate. Visual color comparison is a subjective, qualitative assessment that cannot provide quantitative measurement of active ingredient concentration, as color can be affected by many factors including observer subjectivity. The scientific publication you referenced in the response describes a (b)(4) method for determining (b)(4) values in (b)(4), which is an entirely different matrix, application, and analytical purpose than your (b)(4) product. You conducted preliminary ICP-MS testing, but the laboratory report you provided in the response explicitly states that "the methodology employed was not validated for the matrix" and that "the variability of the results are likely from an inconsistent dissociation of the (b)(4) and cannot be relied upon to determine a quantitative value for (b)(4)."

Related to the AniPrin products, your explanation that microbiological and heavy metal specifications are "controlled using incoming raw material specifications with random verification" is insufficient, and your proposed corrective action to simply remove these specifications from your Certificates of Analysis or add clarifying language does not address the underlying compliance issue.

You are required to establish appropriate and scientifically-sound specifications for your drug products and then to conduct appropriate laboratory testing for conformance to those specifications. See, e.g., 21 CFR 201.22, 211.160, and 211.165.

Moreover, your response lacks a definitive timeline for implementing validated analytical methods, provides no plan for verifying the quality of the product lots already distributed to commerce, and does not include a risk assessment for animals that may have received this inadequately tested product.

Release testing is a critical safeguard that verifies the identity, strength, quality, and purity of drug product batches before they reach the end-user. Without appropriate testing protocols in place, defective products that could cause harm may fail to be identified and rejected.

In response to this letter, provide:

  • A comprehensive, independent assessment of your laboratory practices, procedures, methods, equipment, documentation, and analyst competencies. Based on this review, provide a detailed plan to remediate and evaluate the effectiveness of your laboratory system.
  • Procedure(s) describing how your firm maintains drug product retains (reserve samples) for each batch manufactured at your facility.
  • A list of chemical and microbial specifications, including test methods, used to analyze each batch of your drug products before a batch disposition decision.
    o An action plan and timelines for conducting full chemical and microbiological testing of retain samples to determine the quality of all batches of drug product distributed to the United States that are within expiry as of the date of this letter.
    o A summary of all results obtained from testing retain samples from each batch. If such testing reveals substandard quality drug products, take rapid corrective actions, such as notifying customers and product recalls.
  • The firm name, address, and supplier qualification report for the third-party laboratory or laboratories conducting your drug product release testing.

2. Your firm failed to test samples of each component for identity and conformity with all appropriate written specifications for purity, strength, and quality (21 CFR 211.84(d)).

Your firm failed to ensure that components were suitable for use in the manufacturing of your (b)(4) product. For example, you did not perform identity testing on each lot of incoming components including the active ingredient (b)(4) or the inactive ingredients (b)(4).

Adequate testing is essential for establishing that raw materials—including, but not limited to, active pharmaceutical ingredients—conform to the appropriate specifications prior to their use in drug product manufacturing, including identity testing to detect potential mix-ups that occurred before you received the components. As a manufacturer, you bear the responsibility of sampling, testing, and examining drug components before releasing them for use in production to ensure that adequate quality standards are met.

Your response stated that you sent samples of the active ingredient (b)(4) along with final product lots for ICP-MS testing and were able to confirm through ICP-MS that the final product was approximately (b)(4)% of the (b)(4) raw material. You indicated that you are pursuing USP testing of the raw material with a GMP laboratory, which you expect to be completed within ninety (90) days. You further stated that once you are able to confirm the ability of a GMP laboratory to conduct testing of the (b)(4) raw material, it will fall under your existing SOP titled "Quality Testing of Documented Raw Materials."

Your response is inadequate. The ICP-MS testing you describe was conducted retrospectively, after the raw materials had already been incorporated into finished product that was released and distributed into commerce. You did not describe any interim controls or testing procedures that will be implemented immediately to verify component identity while you establish a relationship with a qualified laboratory. Your response also fails to address the inactive ingredients (b)(4), providing no information about whether identity testing will be performed on these components or whether they will continue to be accepted based solely on supplier COAs.

In response to this letter, provide:

  • A comprehensive, independent review of your material system, including but not limited to:
    o evaluating all suppliers of materials (components, containers, and closures) to determine if they are reliable and appropriately qualified;
    o an assessment of all materials to determine whether they are consistently of acceptable quality;
    o a review to ensure assigned expiration or retest dates are appropriate (supported by data);
    o adequacy of the supplier qualification program, and its selection, qualification, and disqualification provisions.
  • Based on a thorough review, provide a summary of your systems corrective action and preventive action (CAPA) to remediate the supplier qualification program and prevent use of unsuitable components, containers and closures.
  • The chemical and microbiological quality control specifications you use to test and release each incoming lot of component for use in manufacturing.
  • A description of how you will test each component lot for conformity with all appropriate specifications for identity, strength, quality, and purity. If you intend to accept any results from your suppliers’ COAs instead of testing each component lot for strength, quality, and purity, specify how you will robustly establish the reliability of your supplier’s results through initial validation as well as periodic re-validation. In addition, include a commitment to always conduct at least one specific identity test for each incoming component lot.
  • A summary of results obtained from testing all components to evaluate the reliability of the COA from each component manufacturer. Include your SOP that describes this COA validation program.
  • A summary of your program for qualifying and overseeing contract facilities that test the drug products you manufacture.
  • The firm name, address, and supplier qualification report, for your third-party laboratory or laboratories conducting your raw material testing.

3. Your firm failed to establish adequate written procedures for production and process control designed to assure that the drug products you manufacture have the identity, strength, quality, and purity they purport or are represented to possess (21 CFR 211.100(a)).

Your firm failed to qualify the equipment and to validate the processes used to manufacture your (b)(4) product batches, prior to their use in commercial production.

Multiple lots of (b)(4), a (b)(4) agent for wounds, cuts, ulcers, and similar conditions, were released to the market since August 2025 without performing process validation to demonstrate a reproducible commercial manufacturing process that yields a product consistently meeting predetermined specifications and quality attributes.

Process validation evaluates the design integrity and state of control of a manufacturing process throughout its lifecycle. Each significant manufacturing stage must be appropriately designed to ensure the quality of inputs, in-process materials, and finished products. Process qualification studies establish whether an initial state of control has been achieved and must be successfully completed before commercial distribution. Ongoing monitoring of process performance and product quality is then required to maintain a stable manufacturing operation over the product lifecycle.

You responded that you are investigating the initiation of the manufacturing process of the finished product (b)(4) without adequate validation as part of deviation PDP-769U. You indicated that validation was initiated, and the management team was retrained on the relevant SOP. Your response states that as part of the validation, (b)(4) lots of (b)(4) produced since August were tested by ICP-MS to determine the concentration of (b)(4). Further, you indicated that with ICP-MS testing, you were able to confirm that the final product was approximately (b)(4)% of the (b)(4) raw material.

Regarding the equipment qualification, your response was that a deviation (PDP-769U) to SOP PRO-0002.4 Process Change Control has been initiated and that as part of this deviation, you will investigate the implementation of the (b)(4) (ID (b)(4)). Additionally, you indicated that as part of the qualification of the (b)(4), a (b)(4) to measure the rate of (b)(4) was purchased to determine the rate of (b)(4), and a certified thermistor to confirm the temperature of (b)(4). You stated that SOP PRO-0002.4 Process Change Control will be revised.

Your response is inadequate because it fails to demonstrate an understanding of process and equipment validation requirements and does not provide a comprehensive plan to validate your manufacturing process or to verify the quality of products already distributed to commerce.

The equipment qualification plan included in the response is incomplete. While you state that you have purchased a (b)(4) and NIST-certified thermistor, merely purchasing measurement instruments does not constitute equipment qualification. You failed to provide a comprehensive qualification protocol to demonstrate that the equipment consistently performs as intended when manufacturing actual product batches.

The response did not include a validation protocol that defines for example, the number of validation batches to be manufactured, the sampling plans, the analytical methods to be used with appropriate validation, or the statistical approaches for evaluating process capability.

The response addresses only analytical testing of finished products — one component of validation — but fails to address validation of the manufacturing process itself. Using ICP-MS testing on finished product lots as evidence of process validation is scientifically flawed and unacceptable.

The ICP-MS results you provided show significant variability, with (b)(4) concentrations ranging from (b)(4)% across the (b)(4) lots tested, representing more than (b)(4) fold difference. This variability demonstrates that your manufacturing process is not in a state of control and raises questions about whether your products consistently meet the labeled claim of (b)(4) (equivalent to (b)(4)% available (b)(4)). Despite this data, your response provides no explanation for this variability, no investigation into the root causes, and no assessment of whether this variability represents actual differences in product composition or limitations of the analytical method.

In response to this letter, provide:

  • An assessment of each drug product process to ensure that there is a data-driven and scientifically sound program that identifies and controls all sources of variability, such that your production processes will consistently meet appropriate specifications and manufacturing standards. This includes, but is not limited to, evaluating suitability of equipment for its intended use, sufficiency of detectability in your monitoring and testing systems, quality of input materials, and reliability of each manufacturing process step and control.
  • A timeline for performing process performance qualification (PPQ) for each of your marketed drug products. Also provide a risk assessment and any follow-up actions to be taken for the distributed drug products produced without performing any process validation studies.
  • Process performance protocol(s), and written procedures for qualification of equipment and facilities.
  • A detailed program for designing, validating, maintaining, controlling and monitoring each of your manufacturing processes that includes vigilant monitoring of intra-batch and inter-batch variation to ensure an ongoing state of control throughout the product lifecycle. Also, include your program for qualification of your equipment and facility.
  • A comprehensive, independent assessment of your in-process monitoring and sampling operations, focusing on each upstream process step that can introduce variability. Provide your remediation plan to improve: (1) upstream process controls; (2) in-process detection of variation; and (3) sampling plans.

4. Your firm failed to follow your written stability testing program (21 CFR 211.166 (a)).

Your firm has not initiated stability testing to establish appropriate storage conditions and expiration dating for (b)(4). You manufactured and distributed multiple lots of (b)(4) that did not bear an expiration date in the product label.1

Furthermore, stability samples for the following drug products were not tested at the required intervals, and no deviation investigation was initiated: (1) AniPrin P, Lot (b)(4), manufacture date (b)(4), missed the (b)(4) testing which was required on (b)(4); and (2) AniPrin LQ 12% Regular Gallon, Lot (b)(4), manufacture date (b)(4), missed the (b)(4) testing which was required on (b)(4). This is a repeated observation from the previous inspection conducted in March 2022, where similar deficiencies in your stability program were cited.

Stability testing is essential to establish scientifically justified expiration dates and appropriate storage conditions that ensure drug products remain safe and effective from the time of manufacture until the end of their labeled shelf life.

Regarding the lack of stability testing for (b)(4), your response states that at such time as you are able to establish appropriate testing of the (b)(4) content of the product, you will add this to your ongoing stability program. You indicated that once you go forward with production, an expiration date will reflect what you find on stability testing the initial lots (e.g., (b)(4) months, depending on the testing).

Regarding the missed stability testing intervals for AniPrin products, you stated that for AniPrin P, Lot (b)(4), the date the missed (b)(4) sample was required to be tested should be (b)(4), not (b)(4), and that the stability samples for this lot were pulled prior to the previous FDA inspection.

You indicated that in response to the previous inspection, SOP QUA 00019 was changed to pull an additional two samples so that an extra sample is available if one is damaged, and that a deviation has been initiated. For AniPrin LQ 12% Regular Gallon, Lot (b)(4), you stated that a (b)(4) stability sample for this lot was not sent and that a deviation was initiated. You stated that the SOP was updated to include a double check that all samples on the reminder system are included in the laboratory accession form and shipped and that the managers responsible were retrained.

Your response is inadequate. The response does not address the lack of expiration dates on distributed (b)(4) products. It does not describe in detail your stability plan with defined stability conditions, time points, and testing of the appropriate critical quality attributes for drug stability, including but not limited to microbiological and impurity testing. Further, you did not include a comprehensive review of all stability samples to verify that no other missed time points exist and failed to describe how you will verify that your revised procedures are effective in preventing recurrence.

The requirement to establish a stability program is not contingent upon your ability to develop analytical methods; rather, you should not manufacture and distribute a drug product until you have the capability to conduct appropriate stability testing.

Expiration dating must be based on adequate stability data generated under appropriate storage.

In response to this letter, provide:

  • A comprehensive, independent assessment and CAPA plan to ensure the adequacy of your stability program. Your remediated program should include, but not be limited to:
    o Stability indicating methods
    o Stability studies for each drug product in its marketed container-closure system before distribution is permitted
    o An ongoing program in which representative batches of each product are added each (b)(4) to the program to determine if the shelf-life claim remains valid
    o Detailed definition of the specific attributes to be tested at each station (timepoint)
    o All procedures that describe these and other elements of your remediated stability program.
  • The current expiry date for your finished drug products.
  • The firm name, address, and supplier qualification report for the third-party laboratory or laboratories conducting your drug product stability testing.

Unapproved New Animal Drug Violations

Based on our review of your product labeling, your products are drugs under section 201(g)(1) of the Federal Food Drug and Cosmetic Act (FD&C Act) [21 U.S.C. § 321(g)(1)], because they are intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease in animals and/or intended to affect the structure or any function of the body of an animal. For the reasons described below, these products are unapproved new animal drugs and introducing or delivering these products for introduction into interstate commerce is prohibited under section 301(a) of the FD&C Act [21 U.S.C. § 331(a)].

Examples of claims FDA observed on your product labeling that show the intended use of your products as drugs include, but are not limited to, the following:

(b)(4)

  • "(b)(4)."

AniPrin P

  • “Aids in relieving minor muscle and joint pain.”
  • “…an aid in reducing fever”
  • “…relief of minor muscle aches… pains in horses.”
  • “…Reproductive Harm…”
  • “...analgesic”
  • “...antipyretic”

Rot-B-Gone

  • “...If redness, irritation,..swelling persist, discontinue use.”

Your products are new animal drugs under section 201(v) of the FD&C Act, [21 U.S.C. § 321(v)], because they are not generally recognized, among experts qualified by scientific training and experience to evaluate the safety and effectiveness of animal drugs, as safe and effective for use under the conditions prescribed, recommended, or suggested in the labeling.

To be legally marketed, a new animal drug must have an approved new animal drug application, conditionally approved new animal drug application, or index listing under sections 512, 571, and 572 of the FD&C Act [21 U.S.C. § 360b, 360ccc, and 360ccc-1]. These products are not approved or index listed by FDA, and therefore, the products are unsafe within the meaning of section 512(a) of the FD&C Act, [21 U.S.C. § 360b(a)], and adulterated under section 501(a)(5) of the FD&C Act [21 U.S.C. § 351(a)(5)]. The introduction or delivery for introduction into interstate commerce of an adulterated drug is prohibited under section 301(a) of the FD&C Act [21 U.S.C. § 331(a)].

CGMP Consultant Recommended

Based upon the nature of the violations we identified at your firm, you should engage a consultant qualified as set forth in 21 CFR 211.34 to evaluate your operations and to assist your firm in meeting CGMP requirements. The qualified consultant should also perform a comprehensive six-system audit2 of your entire operation for CGMP compliance and evaluate the completion and efficacy of your corrective actions and preventive actions before you pursue resolution of your firm’s compliance status with FDA.

Your use of a consultant does not relieve your firm’s obligation to comply with CGMP. Your firm’s executive management remains responsible for resolving all deficiencies and systemic flaws to ensure ongoing CGMP compliance.

Conclusion

The violations cited in this letter are not intended to be an all-inclusive list of violations that exist at your facility. You are responsible for investigating and determining the causes of any violations and for preventing their recurrence or the occurrence of other violations.

You must correct any violations promptly. Failure to promptly and adequately address this matter may result in regulatory or legal action without further notice, including, without limitation, seizure and injunction. Unresolved violations may also prevent other Federal agencies from awarding contracts.

FDA may withhold approval of new applications or supplements listing your firm as a drug manufacturer until any violations are completely addressed and we confirm your compliance with CGMP. We may re-inspect to verify that you have completed corrective actions to any violations.

This letter notifies you of our findings and provides you with an opportunity to address the above deficiencies. After you receive this letter, respond to this office in writing within 15 working days. Specify what you have done to address any violations and to prevent their recurrence. In response to this letter, you may provide additional information for our consideration as we continue to assess your activities and practices. If you cannot complete corrective actions within 15 working days, state your reasons for delay and your schedule for completion.

Send your electronic reply to CVM-483-Responses@fda.hhs.gov. Refer to the CMS Case number 728604 FEI 3002745172 and ATTN: Dayna I. Martínez when replying.

Sincerely,
/S/

Johnetta Walters, Ph.D.
Acting Director
Division of Drug Compliance
Office Surveillance and Compliance
Center for Veterinary Medicine

___________________

1 See also, 21 CFR 211.137.

2 i.e., Quality System, Facilities & Equipment System, Materials System, Production System, Packaging & Labeling System, and Laboratory Control System per FDA’s guidance document Quality Systems Approach to Pharmaceutical CGMP Regulations.

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