THE INFLUENCE OF OSTERTAGIA-CIRCUMCINCTA AND TRICHOSTRONGYLUS-COLUBRIFORMIS INFECTIONS ON THE PHARMACOKINETICS OF FEBANTEL IN LAMBS

Plasma concentrations of febantel and its major metabolites fenbendazole, oxfendazole and oxfendazole sulphone were determined after oral administration of 7.5 mg/kg febantel in lambs before and 28 days after infection with 50 000 L3 larvae of Ostertagia circumcincta or Trichostrongylus colubriformis. The febantel concentrations were always very low and only in a few samples higher than the detection limit. The mean decrease in AUC for the three metabolites for the infected sheep in comparison to the parasite naive sheep was 13.9% +/- 4.1% (mean +/- SEM) and 23.7% +/- 5.3% in the O. circumcincta infected and the T. colubriformis infected lambs respectively. This reduction was only significant for the T. colubriformis infected group. In order to determine a more complete pharmacokinetic profile, febantel was injected intravenously at a dose of 2.5 mg/kg in a further study.