Which drug may be used extralabel, in some circumstances, in a food-producing animal?

• A. Clenbuterol
• B. Phenylbutazone
• C. Vancomycin
• D. Diethylstilbestrol

Answer: (B)

Extralabel drug use in food-producing animals is tightly regulated and can be permitted only under the Animal Medicinal Drug Use Clarification Act (AMDUCA) when there is no approved drug for the condition in that species, the clinician judges the use medically necessary, and a safe withdrawal period can be established to protect the food supply. The drug and its dose, duration, and route must be justified by veterinary judgment and supported by relevant literature, with proper recordkeeping and a valid veterinarian–client–patient relationship.

In this context, phenylbutazone is the one that may be used extralabel in some circumstances because, as an NSAID with veterinary precedent, it can be considered under AMDUCA if no approved alternatives exist and withdrawal times can be observed. The other listed drugs are not used extralabel in food-producing animals: clenbuterol is prohibited due to the risk of harmful residues; vancomycin is a critical human medicine not to be used extralabel in animals producing food; and diethylstilbestrol is banned because of serious safety and reproductive risks.