Pharmacokinetics of albendazole in sheep.

The concentrations of albendazole and its two major metabolites, the sulfoxide and sulfone, were measured in plasma and in ruminal and abomasal fluid of three sheep (surgically prepared with permanent ruminal and abomasal cannulae) orally given albendazole as a suspension at a dose rate of 10 mg/kg. Albendazole was not detectable in plasma at any time in one sheep (detection limit, 0.02 micrograms/ml) and in the other sheep, only transiently detectable. Albendazole sulfoxide was detectable in plasma and in abomasal fluid at mean peak concentrations of 3.2 and 26.2 micrograms/ml, respectively, 20 hours after administration. It is probable that much of the anthelmintic activity of albendazole in sheep is due to the metabolically formed sulfoxide and sulfone.