Ivermectin residues in the edible tissues of swine and cattle: effect of cooking and toxicological evaluation.

Young male pigs (25-40 kg bw) were treated experimentally with a single 0.4 mg/kg bw, s.c. dose of ivermectin (Ivomec vet. inj., MSD). The disappearance of the drug from the edible tissues 7-21 days after treatment was studied using a sensitive high-performance liquid chromatographic method. The highest residue levels were found at the injection site (up to 59 and 2.6 mg/kg 7 and 14 days post-injection, respectively). Among the other tissues studied, the residue levels 7 days post-injection showed the following order: liver (less than or equal to 50 micrograms/kg) greater than kidney (less than or equal to 25 micrograms/kg) greater than muscle (less than or equal to 20 micrograms/kg). After 21 days only traces of ivermectin (less than or equal to 2 micrograms/kg) could be detected in the muscle and other edible tissues, including the injection site. Similar residue concentrations were found in slaughterhouse material from sows therapeutically treated with ivermectin for parasite infestation. An ordinary culinary preparation of the minced beef muscle from a bull treated with ivermectin resulted in a 45% (boiling) or 50% (frying) decrease in the drug residue. Based on the known toxic effects of the drug and the results of the present and other residue studies, the suggested withdrawal time for Ivomec in edible tissues of swine and cattle is 21 and 28 days, respectively.