Comparative efficacy of albendazole against Fasciola hepatica in sheep and calves: relationship to serum drug metabolite levels.

Calves were given albendazole (ABZ) daily in feed at levels of 0,3 or 5 mg kg-1 day-1. None of the ABZ treatment levels was significantly effective in reducing Fasciola hepatica burdens. A dose rate of 5 mg kd-1 day-1 did significantly reduce the fecal egg count. Measurements of serum drug levels from calves following a single dose of ABZ showed ABZ levels to be low, but sulfoxide and sulfone metabolites of ABZ were present in (significant) larger quantities. The total available sulfoxide present in calves, however, was much lower than in sheep receiving the same dose of ABZ. Measurements of serum metabolite levels from sheep and calves which were given daily low-level doses of ABZ also indicated that the serum sulfoxide levels of calves were much lower than those of sheep receiving the same ABZ dose. These results indicated that ABZ is not an effective prophylactic treatment for bovine fascioliasis and the differences in efficacy between sheep and cattle correlated with the differences in serum metabolite levels.