COMPARATIVE KINETIC DISPOSITION OF OXFENDAZOLE IN SHEEP AND GOATS BEFORE AND DURING INFECTION WITH HAEMONCHUS-CONTORTUS AND TRICHOSTRONGYLUS-COLUBRIFORMIS

The kinetic disposition of [C-14]-oxfendazole (OFZ) and its metabolite s, fenbendazole (FBZ) and fenbendazole sulphone (FBZ.SO2), in plasma a nd abomasal fluid were determined in Merino sheep and Angora goats bef ore and during infection with Trichostrongylus colubriformis and Haemo nchus contortus. The systemic availability (area under the plasma curv e, AUC) of OFZ was significantly lower in goats (13.5 mug.h/ml) than i n sheep (22.2 mug.h/ml) and was reduced with infection in goats (5.6 m ug.h/ml) and sheep (15.1 mug.h/ml). The elimination of plasma [C-14] w as faster in goats than in sheep. The responses observed for [C-14] we re a reflection of the behaviour of OFZ. The concentration of OFZ and metabolites in abomasal fluid were similar in both species in the abse nce or presence of infection. However, as the mean flow rate of abomas al fluid was slower in goats (240 ml/h) than in sheep (488 ml/h), only 7% of the dose passed the pylorus in abomasal fluid of goats compared with 14% in sheep. The presence of gastrointestinal nematodes general ly increased abomasal fluid flow rate but neither species nor infectio n had any effect on the rate or extent of [C-14] excretion in urine or faeces. It is suggested that goats possess a faster hepatic metabolis m than sheep resulting in more rapid elimination of OFZ.