Drug compounding can be defined as the art and science of mixing ingredients, which may be active, inactive or both, to create a specific dosage form to meet a specific patient’s needs. Compounding can be performed by a veterinarian or by a pharmacist upon receipt of a veterinarian's prescription. A veterinarian must have a valid veterinarian-client-patient relationship (VCPR ) to legally prescribe or prepare a compounded product. Federal regulations require that legally compounded drugs meet a number of criteria including:

• A valid VCPR must exist.

• There must be no Food and Drug Administration (FDA)–approved, commercially available animal or human drug that when used as labeled or in an extra-label fashion in its available dosage form and concentration will appropriately treat the patient.

• The product must be compounded by a licensed veterinarian or a licensed pharmacist on the order of a veterinarian within the practice of veterinary medicine.

• Veterinarians must comply with all aspects of the federal extra-label drug use regulations, including recordkeeping and labeling requirements.

Pharmacies specializing in veterinary compounding have been growing exponentially, aided by the ability to reach a larger number of consumers via the Internet. Many commercial websites market directly to the owner, offering subjective treatments based on testimonials and compounded therapies that are not permitted by the criteria established for compounded drugs. Currently, the FDA does not have the resources to enforce these regulations; however, veterinarians should be aware that abuse of these regulations can result in legal actions.

Compounded drugs are not the same as generic drugs. Generic drugs are FDA approved and must have bioequivalence to the "pioneer brand name" drug. Generic drugs can be identified by the Abbreviated New Animal Drug Application (ANADA) number on their label and by cross-checking in the FDA Green Book of Approved Animal Drug Products. In contrast, compounded drugs are spontaneously prepared products that lack FDA approval.

The idea is that compounded drugs with their possible inadequacies are better than no drug at all and suitable for a small patient population. Equine practitioners using compounded products are put in a position of evaluating the integrity of the compounding pharmacy as well as the quality and consistency of the pharmaceuticals they produce. The FDA does not routinely inspect compounding pharmacies. This lack of regulatory oversight means that almost none of the veterinary compounding pharmacies follow Good Manufacturing Practices (GMPs) guidelines. GMP training and protocol are not required of compounding pharmacies because they are not authorized to "manufacture" drug products. In some instances, loose oversight has allowed negligent compounders to prepare products from unregulated raw materials with no quality standards. Many of these raw materials are chemical grade bulk products that were never intended for use in the preparation of legitimate pharmaceuticals. Other compounding pharmacies distribute medication without a valid prescription. Veterinarians are schooled on quality patient care, but few pharmacists receive training in quality control for pharmaceutical production