In recent years, the availability of illegal clenbuterol formulations, produced as "compounded" drug product, has increased steadily, according to a Jan. 10 update issued by the Food and Drug Administration's Center for Veterinary Medicine. The agency warns veterinarians that prescribing, purchasing, or distributing "compounded" clenbuterol is in violation of federal law. Veterinarians ultimately assume responsibility for the efficacy, safety, and composition of drugs prescribed in this manner.

The FDA has special concern over clenbuterol, a beta-agonist drug that has been used illegally in the United States to enhance food animal production. Other countries have documented adverse reactions in people who ingested meat with clenbuterol residues.

The only clenbuterol product approved for use in the United States is Ventipulmin, a restricted use, prescription-only drug for treating horses with airway obstruction. This syrup, produced by Boehringer Ingelheim Vetmedica Inc., contains a small amount of clenbuterol.

Under the Animal Medicinal Drug Use Clarification Act, compounding is permitted only under limited circumstances. Other criteria required under AMDUCA include observing prohibitions against use of some drug products in food animals, and establishing the need for a compounded product. When an approved product is available, use of a compounded product is not permitted unless it meets the AMDUCA criteria.

AMDUCA does not permit compounding from bulk drugs. In the case of clenbuterol, the FDA stated that bulk supplies should be available only to the manufacturer of the approved clenbuterol product. Clenbuterol products that mimic the approved product are considered unapproved new animal drugs and are not legal for preparation, sale, or use. The manufacturer has provided information to the FDA demonstrating the existence of compounded clenbuterol products that are copies of the FDA-approved product.

The FDA said it will consider enforcement action for any preparation, advertising, sale, and use of unapproved clenbuterol.