Pharmacokinetics of fenbendazole in dogs

McKellar, Q.A., Harrison, P., Galbraith, E.A. & Inglis, H. Pharmacokinetics of fenbendazole in dogs. J. vet. Pharmacol. Therap. 13, 386–392. Fenbendazole was administered to dogs at a dose rate of 20 mg/kg body weight on a single occasion in gelatin capsules, on 5 consecutive days in feed, and on a single occasion as an alginate suspension. It was also administered at a dose rate of 100 mg/kg body weight on a single occasion in feed. Following single administration of 20 mg/kg fenbendazole mean maximum concentrations (C max ) of the parent drug and its known active sulphoxide metabolite were 0.42 ± 0.05 and 0.31 ± 0.05 μg/ml, respectively. Mean times until maximum concentrations were achieved (t max ) were 12.67 ± 4.18 and 15.33 ± 2.81 h, respectively, and areas under the plasma concentration‐time curves (AUC) were 5.83 ± 0.65 and 4.60 ± 0.57μg.h/ml, respectively. Administration in feed increased the apparent bioavailability and administration for 5 consecutive days provided sustained plasma concentrations, generally > 0.2μg/ml. Administration as an alginate did not increase bioavailability or extend the persistence in plasma. It did increase the t max to 16.80 ± 2.93 and 20.00 ± 2.53 h for fenbendazole and its sulphoxide metabolite, respectively. Increasing the dose from 20mg/kg to 100mg/kg did not substantially increase the C max or AUC.Q. A. McKellar, Department of Veterinary Pharmacology, University of Glasgow Veterinary School, Bearsden Road, Bearsden, Glasgow G61 1QH, UK.