Effect of diet variations on the kinetic disposition of oxfendazole in sheep

Pharmacokinetic parameters of oxfendazole (OFZ) were determined in five sheep submitted to two different feeding regimens: a poor/dry diet based on wheat straw ad libitum, and a rich/green diet based on fresh grass grazed on pasture. Animals were acclimatised to each diet before they were administered OFZ orally at a dose of 5 mg kg-1 body weight. Blood samples were taken serially between 10 min and 168 h post-administration. Plasma concentrations of OFZ and its metabolites (fenbendazole (FBZ) and fenbendazole sulphone) were quantified using an HPLC technique. Rates of absorption of OFZ and of formation of FBZ and fenbendazole sulphone were slower with the poor/dry diet; however, the area under FBZ plasma concentration vs time curve was higher when sheep were offered the low quality diet, suggesting a shift of OFZ metabolism towards FBZ formation.