Phenylbutazone use surveyed, caution advised

The Department of Agriculture has not been testing specifically for phenylbutazone residues in dairy cows, despite a history of violations and development of an advanced screening test for the compound.

According to Food Chemical News (Sept.10), last year the USDA and the Food and Drug Administration collaborated to survey how widely the drug was being used in the field by testing the new screen in cull (market) dairy cow plants. Phenylbutazone residues were found in 13 of 2,243 cull cows (a 0.05 percent failure rate) over six months. The compound, which has been linked to serious medical problems in sensitive human consumers, has not been approved for use in food animals.

The government has a zero tolerance policy for this drug.

The FDA gave the new screening test to the USDA May 5 for use in the field, after the survey was completed, but the department has yet to begin using the test. The agency is able to find phenlybutazone by using one of its pesticide residue tests, but that test takes more time and is far less sensitive than the new method.

The states and the FDA conducted investigations for all of the violations. Some violators were veterinarians, who use this drug in food animals on an extralabel basis.

At press time, meat industry officials were urging the government to ban phenylbutazone outright in food-producing animals, but the FDA was not considering withdrawing its approval.

The FDA says it will do whatever it can, however, to keep the drug from entering the food supply in the form of residues when those administering the compound do not observe proper withdrawal times.

Food Chemical News reported that the FDA and USDA also looked at how widely flunixin meglumine, another anti-inflammatory drug, might be abused in the field. A separate survey conducted by the agencies found 11 violations for flunixin out of 380 cull cows. In recent months, the USDA has begun implementing the new screening test for this drug in the field.

The Food Animal Residue Avoidance Databank strongly discourages the use of phenylbutazone in any food animal species, citing food safety data and legal requirements of extralabel drug use.

Practitioners are reminded that when treating food animals with drugs in an extralabel fashion, they must preferentially use an effective drug bearing a food animal label over a human or companion animal drug.

Because phenylbutazone can be detected in the urine of treated animals for extended periods after treatment, FARAD estimates the slaughter withdrawal interval for IV, extralabel phenylbutazone administration in cattle (up to 4.4 mg/kg) to be 45 days and the milk withholding interval to be 120 hours.

In contrast, the slaughter withdrawal time for labeled IV use of flunixin meglumine in beef cattle is four days. FARAD recommends using the label slaughter withdrawal interval of four days for lactating dairy cattle, and estimates the milk withholding interval following extralabel, IV administration of flunixin meglumine to be 72 hours.