Pharmacokinetics of fenbendazole following intravenous and oral administration to pigs

Objective-To determine pharmacokinetics and metabolic patterns of fenbendaz ole after IV and oral administration to pigs. Animals-4 mixed-breed female pigs weighing 32 to 45 kg. Procedure-Fenbendazole was administered IV at a dose of 1 mg/kg. One week l ater, it was administered orally at a dose of 5 mg/kg. Blood samples were c ollected for up to 72 hours after administration, and plasma concentrations of fenbendazole, oxfendazole, and fenbendazole sulfone were determined by use of high-pressure liquid chromatography. Plasma pharmacokinetics were de termined by use of noncompartmental methods. Results-Body clearance of fenbendazole after IV administration was 1.36 L/h /kg, volume of distribution at steady slate was 3.35 L/kg, and mean residen ce time was 2.63 hours. After oral administration, peak plasma concentratio n of fenbendazole was 0.07 mu g/ml, time to peak plasma concentration of fe nbendazole was 3.75 hours, and mean residence time was 15.15 hours. Bioavai lability of fenbendazole was 27.1%. Oxfendazole was the major plasma metabo lite, accounting for two-thirds of the total area under the plasma concentr ation versus lime curve after IV and oral administration. Fenbendazole acco unted for 8.40/0 of the total AUC after IV administration and 4.5% after or al administration. Conclusions and Clinical Relevance-Results indicate that fenbendazole was r apidly eliminated from plasma of pigs. The drug was rapidly absorbed after oral administration, but systemic bioavailability was low.