Mebendazole concentrations in sheep plasma

Formulated mebendazole was administered to sheep by intraruminal injection at dose rates of 12.5, 25, 50 or 100 mg/kg bodyweight. The concentrations of mebendazole and two major metabolites were measured by high-performance liquid chromatography in plasma taken at intervals up to 48 hours after treatment. At 12.5 mg/kg the peak plasma concentration was 0.22 +/- 0.03 microM mebendazole, rising to 0.76 +/- 0.04 microM at 100 mg/kg. Peak plasma concentrations occurred between nine and 24 hours for all dose rates and declined rapidly. Two major metabolites were detected; their concentrations exceeded that of mebendazole at all dose rates.