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

Plasma concentrations of febantel and its major metabolites fenbendazo le, oxfendazole and oxfendazole sulphone were determined after oral ad ministration of 7.5 mg/kg febantel in lambs before and 28 days after i nfection with 50 000 L3 larvae of Ostertagia circumcincta or Trichostr ongylus colubriformis. The febantel concentrations were always very lo w 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 co mparison 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. colubri formis infected lambs respectively. This reduction was only significan t for the T. colubriformis infected group. In order to determine a mor e complete pharmacokinetic profile, febantel was injected intravenousl y at a dose of 2.5 mg/kg in a further study.