The influence of a heavy infection with sensitive and resistant strains ofOstertagia circumcinctaand withTrichostrongylus colubriformison the pharmacokinetics of febantel in lambs

摘要

Plasma concentrations of febantel and its major metabolites, fenbendazole, oxfen‐dazole and fenbendazole sulphone, were determined after oral administration of 7.5 mg/kg febantel in lambs before and 28 days after infection with 100 000 L3 larvae of a benzimidazole (BZ)‐ sensitive or BZ‐resistant strain ofOstertagia circumcinctaor with 75 000 L3 larvae of a BZ‐ sensitiveTrichostrongylus colubriformisstrain. The febantel concentrations were always low, and in only a few samples were higher than the limit of detection. A mean decrease in the area under the curve (AUC) for the three metabolites of 10.2, 16.4 and 4.9 in lambs infected, respectively, with BZ‐sensitive O.circumcincta, BZ‐resistantO. circumcinctaandT. colubriformiswas observed. TheCmaxfor all the metabolites was higher in the BZ‐sensitive O.circumcinctagroup than in the naive sheep, while theTmaxoccurred earlier. TheCmaxand theTmaxvalues for all the metabolites were lower in the BZ‐resistant O.circumcinctagroup than in their own naive controls. In the T.colubriformisgroup the Cmaxvalues of the metabolites were lower and the Tmaxoccu