Comparative microsomal oxidation of febantel and its metabolite fenbendazole in various animal species.

A comparison has been made of the in vitro metabolism of febantel (FBT) with that of one of its pharmacologically active metabolites fenbendazole (FBZ) using microsomal preparations from liver of sheep, calf, horse, pig, rat, chicken and trout. The oxidation of FBT to the corresponding sulphoxide appeared to be far more rapid with the exception of the trout, than a similar reaction with FBZ. Indeed FBT was further metabolized in several species by cyclization and further oxidation. This observation could have toxicological significance in view of the greater tetratogenic effects of the metabolite oxfendazole. Reaction rates were most rapid in pigs and sheep.