Influence of diet type on the kinetic disposition of fenbendazole in cattle and buffalo.

The plasma concentration profiles of fenbendazole (FBZ), FBZ-sulphoxide and FBZ-sulphone were measured following intraruminal administration of FBZ at 7.5 mg kg-1 body weight in cattle and buffalo offered 3 different diets: 100% dry mature sorghum hay, 100% green Pennisetum spp. and a 50:50 mix of these 2 diets. Changing the diet from dry to green fodder resulted in significantly lower systemic availability of FBZ and its metabolites in both species. Buffalo had a lower systemic availability of the drug than cattle on the dry diet and the difference between species increased when the diet included green fodder. It is suggested that decreased transit time of digesta on the green fodder reduced systemic concentrations by reducing the time available for gastrointestinal absorption of the drug.