Plasma Concentrations of fenbendazole (FBZ) and oxfendazole in alpacas (Lama pacos) after single intravenous and oral dosing of FBZ

Abstract

The objective of this study was to determine plasma pharmacokinetics and bioavailability of fenbendazole (FBZ) and oxfendazole (OZF) after i.v. and oral administration of FBZ (5 mg/kg) to alpacas. Plasma concentrations FBZ and OZF after administration of FBZ i.v. and orally (5 mg/kg) were determined by HPLC-UV. Total clearance (CL) of FBZ was 16.5 ± 4 mL/kg/min (range: 4 - 31 mL/kg/min), and steady-state volume of distribution (Vdss) was 3.3 ± 1 L/kg (range: 1.7-7.4 L/kg). The terminal phase half-life of FBZ after i.v. administration of was 5.9 ± 3.8 h (range 0.8 - 20 h). After oral administration, the FBZ terminal phase half-life was 23 ± 5 h (range: 9 - 37 h) and the systemic bioavailability of FBZ was 16 ± 6 % (range: 1 - 41%). Peak FBZ concentrations after oral administration were 0.13 ± 0.05 µg/mL (range 0.05 - 0.28 µg/mL) at 10 h (range 8 - 12 h). Peak plasma OZF concentrations after oral dosing with FBZ (5 mg/kg) were 0.14 ± 0.05 µg/mL (0.05 - 0.3 µg/mL) at 24 ± 7 h (range: 12 - 48 h). Fenbendazole clearance is lower in comparison to other species. Systemic availability of FBZ after oral administration is low after oral dosing. Metabolites of FBZ produced by alpacas are similar to that observed in other species.