Sulfa residues in pork: an update

Sulfamethazine (SMZ) is an antibacterial drug used in approximately 75% of all hogs marketed in the U.S. The tolerance for residues of SMZ in uncooked tissues is .1 ppm, and the withdrawal time is 15 d. The rate of illegal residues in swine from the use of SMZ has continued to fluctuate between 4% and 5% from 1980 through 1987. This was not acceptable. The Center for Veterinary Medicine (CVM) also has received from the National Center for Toxicological Research a report showing that SMZ produces a dose-related increase in follicular cell adenomas of the thyroid gland in rats and mice. The FDA has discovered three major causes of SMZ residues by investigating violators. The number one cause was a lack of sequencing, flushing, and cleaning of mixer equipment. Failure to follow withdrawal times was another major cause, and the third major reason was the use of a soluble powder solution. At least 16% of SMZ residue violations have resulted in no follow-up due to lack of animal identification. The FDA district offices are conducting on-farm investigations of swine producers who have caused SMZ violations. Repeat violators and those that produce higher residue levels will receive a higher priority. The FDA currently is attempting to obtain more state support, particularly for investigation of first-time violators. The CVM is serious about resolving the SMZ residue problem.