Metabolic disposition of ivermectin in swine

Tissue residue distribution and metabolism of tritium-labeled ivermectin have been studied in swine dosed subcutaneously at 0.4 mg/kg of body weight. The residue distribution pattern among edible tissues (liver, kidney, muscle, and fat) was similar to those found in cattle, sheep, and rats, with highest levels in fat and liver tissues ranging between 78 and 654 ppb within ppb within 7 days after dosing. The parent drug was the major radioactive residue in liver and fat, accounting for >50% of total radioactivity up to 7 days and {approximately}30% after 14 days. The major liver metabolites were identified as 3{double prime}-O-desmethyl-H{sub 2}B{sub 1a} and 3{double prime}-O-desmethyl-H{sub 2}B{sub 1b} by chemical derivatization and mixed-sample HPLC cochromatography with in vitro metabolites from swine liver microsomal incubations. As in other species studied, good correlation has been observed between in vitro and in vivo metabolism. The drug was essentially eliminated by fecal and biliary excretion.