The Food and Drug Administration has issued an order prohibiting extralabel use of phenylbutazone (animal and human drugs) in female dairy cattle 20 months of age or older. The FDA took this action because of evidence that such use presents a risk to the public health. The proposed order, published in the Feb. 28, 2003, Federal Register, will become effective May 29, 2003, unless the FDA revokes or modifies the order or extends the comment period.

The AVMA welcomes the announcement. Through the Council on Biologic and Therapeutic Agents, the AVMA examined residue surveillance data and, in 2002, recommended to the FDA that it focus its intended prohibition of the drug where it is needed, while permitting drug use in instances where no food safety concerns exist.

Phenylbutazone became available for use in humans for the treatment of rheumatoid arthritis and gout in 1949. Currently, however, it is not approved or marketed for any human use in the United States, because some patients treated with the drug have experienced severe toxic reactions. In addition, other effective, less toxic drugs are now available to treat the same conditions.

Phenylbutazone is known to induce blood dyscrasias, including aplastic anemia, leukopenia, agranulocytosis, and thrombocytopenia, and can result in death. Hypersensitivity reactions of the serum-sickness type have also been reported. In addition, phenylbutazone is a carcinogen, as determined by the National Toxicology Program.

For animals, phenylbutazone is currently approved only for oral and injectable use in dogs and horses. It is not approved for use in any food-producing animal, and its labeled use in horses is limited to horses not intended for food.

Investigation by the FDA and state regulatory counterparts, however, has found phenylbutazone on farms and identified tissue residues in market dairy cattle. The Department of Agriculture's Domestic National Residue Monitoring Program tests between 400 and 500 market dairy cattle per year. The USDA found zero violations for phenylbutazone residues in 2002 and 2001, one in 2000, and zero in 1999 and 1998. In a special project performed by the USDA and FDA, however, looking over a six-month period spanning late 2000 through early 2001, a 0.5 percent violation rate was discovered. Thus, the FDA sees the ban as necessary to protect public health.

In 1994, the Animal Medicinal Drug Use Clarification Act amended the Federal Food, Drug, and Cosmetic Act to allow licensed veterinarians to prescribe extralabel uses of approved animal drugs and human drugs in animals. The FDA, however, was given the power to prohibit an extralabel drug use, if, after affording an opportunity for public comment, the agency found that the use presented a risk to the public health. The agency, in this case, is exercising this power.

The FDA will consider all comments received by April 29, 2003. Written comments should be submitted to the Dockets Management Branch (HFA-305), FDA, 5630 Fishers Lane, Room 1061, Rockville, MD 20852. Submit electronic comments to www.fda.gov/dockets/ecomments.

For more information, read the full announcement in the Federal Register, www.fda.gov/OHRMS/DOCKETS/98fr/03-4741.htm, or contact Gloria J. Dunnavan, CVM (HFV-230), FDA, 7500 Standish Place, Rockville, MD 20855; (301) 827-1168, or gdunnava@cvm.fda.gov.