1. The in vivo S-oxidation of
albendazole was measured from the pharmacokinetic profile of
albendazole sulphoxide and sulphone determined in young male sheep receiving oral
albendazole (1.9 mg/kg). Studies were carried out before, and each month after, oral infestation by 150 metacercariae of Fasciola hepatica. 2. Parasitic pathology was ascertained by clinical observation of animals, and the increase in plasma
antibodies directed against liver flukes. 3. Rate of conversion of
sulphoxide to sulphone and rate of sulphone elimination, were respectively decreased by 47% and 87% at week 8 post-
infection, whereas significant increases in the area under plasma sulphone concentrations versus time curve and mean residence time, occurred 4-12 weeks following the infestation. 4. A 58% decrease in
albendazole sulphonation was demonstrated in liver microsomal preparations obtained from 8-week-infected sheep, while there was no change in the
FAD-directed sulphoxidation of
albendazole. 5. The transient impairment of
albendazole sulphonation could be related to the decrease in liver microsomal
cytochrome P450-dependent
monooxygenases observed in sheep with a similar parasitic pathology.