Veterinary Warning Letters

FDA Warning Letter to AHC Products, Inc. for CGMP Violations

The U.S. Food and Drug Administration (FDA) has issued a Warning Letter to AHC Products, Inc. of Winchester, Kentucky, citing significant violations of Current Good Manufacturing Practice (CGMP) regulations for finished pharmaceuticals and alleging that the company marketed several unapproved new animal drugs.

Following an inspection conducted in October 2025, FDA concluded that the firm’s methods, facilities, and manufacturing controls did not conform to CGMP requirements, causing its animal drug products to be adulterated under the Federal Food, Drug, and Cosmetic Act. The agency also cited several products, including AniPrin P and Rot-B-Gone, as unapproved new animal drugs marketed without the required FDA approvals.

FDA Identifies Fundamental Manufacturing Deficiencies

The Warning Letter describes deficiencies spanning multiple elements of pharmaceutical quality systems, including laboratory controls, raw material testing, process validation, stability testing, supplier qualification, and product release.

Among FDA’s most significant findings was that AHC Products released multiple batches of finished animal drugs without performing laboratory testing to confirm that the products met final specifications before distribution. In some cases, FDA said release decisions relied solely on visual assessment rather than scientifically validated analytical testing.

The agency also found that Certificates of Analysis reported microbiological and heavy metal results for certain products even though the corresponding finished-product testing had not been performed.

FDA rejected the firm’s explanation that visual color comparison could adequately estimate active ingredient concentration, stating that such assessments are subjective and cannot replace validated analytical methods required to verify product identity, strength, quality, and purity before release.

Supplier Controls and Component Testing

The agency also cited AHC Products for failing to perform identity testing on incoming lots of active and inactive ingredients before they were used in manufacturing.

FDA emphasized that manufacturers, not suppliers, bear responsibility for verifying that incoming materials meet established quality specifications. The Warning Letter calls for a comprehensive review of the firm’s supplier qualification program, raw material controls, and procedures governing the acceptance of supplier Certificates of Analysis.

Process Validation and Stability Programs

FDA further alleged that the company commercially manufactured and distributed certain products without first validating its manufacturing processes or qualifying production equipment.

According to the agency, subsequent analytical testing revealed significant variability between production lots, raising questions about whether the manufacturing process was capable of consistently producing products meeting labeled specifications.

FDA also criticized the firm’s reliance on finished-product testing as a substitute for process validation, noting that process validation must demonstrate that manufacturing consistently produces acceptable product and not simply measure the characteristics of finished batches.

The Warning Letter also cites deficiencies in the firm’s stability program, including products distributed without expiration dates and missed stability testing intervals for marketed products. FDA noted that similar stability deficiencies had been identified during a previous inspection in 2022.

FDA Recommends Independent CGMP Review

Given the breadth of the deficiencies, FDA recommended that AHC Products retain a qualified CGMP consultant to conduct a comprehensive six-system audit covering the firm’s Quality System, Facilities and Equipment, Materials, Production, Packaging and Labeling, and Laboratory Control systems. The agency stressed that while outside expertise may assist remediation efforts, executive management remains responsible for achieving and maintaining CGMP compliance.

MDP Perspective

This Warning Letter illustrates that FDA’s expectations for animal drug manufacturers mirror those applied throughout the pharmaceutical industry. Current Good Manufacturing Practice requirements are designed to ensure that every batch of drug product consistently meets established standards for identity, strength, quality, and purity before reaching the marketplace.

Equally notable is the breadth of FDA’s observations. Rather than identifying a single isolated deficiency, the agency cited concerns involving laboratory controls, supplier qualification, process validation, stability testing, and product approval requirements. Together, these observations point to systemic weaknesses across multiple quality system elements.

The Warning Letter also reinforces a fundamental principle of pharmaceutical manufacturing: manufacturers are ultimately responsible for demonstrating that both incoming materials and finished products meet scientifically established specifications. Supplier documentation may support that process, but it does not replace the manufacturer’s obligation to establish appropriate controls, validate manufacturing processes, and verify product quality before release.

For regulatory and quality professionals, the case serves as another reminder that effective CGMP compliance depends on an integrated quality system in which laboratory controls, supplier oversight, process validation, and stability programs work together to provide objective evidence that products consistently meet regulatory requirements.