DETERMINATION OF IVERMECTIN LEVELS IN SWINE TISSUES AT THE PARTS-PER-BILLION LEVEL BY LIQUID-CHROMATOGRAPHY WITH FLUORESCENCE DETECTION

Ivermectin levels in swine tissues have been determined by an HPLC/fluorescence detection method, originally used to determine levels in sheep and cattle tissues. The method involves homogenization, centrifugation, and several liquid-liquid solvent partition steps. The recovery of ivermectin at levels between 6 and 150 ppb in kidney, liver, fat, and muscle averaged 85%, with a quantitation limit of 5 ppb and a limit of detection of 1 ppb. Good agreement was observed between this method and a reverse isotope dilution method. The method was further used to determine ivermectin levels in edible swine tissues, where swine were dosed by subcutaneous injection and in feed. The ivermectin distribution pattern showed high levels in fat and liver and an overall rapid depletion in all tissues. The suggested withdrawal time for swine dosed at 2 ppm for 7 days in feed is 5 days, and that for swine dosed at 0.4 mg/kg subcutaneously is 18 days.