COMPARATIVE PHARMACOKINETICS OF FENBENDAZOLE IN BUFFALO AND CATTLE

Swamp buffalo (Bubalus bubalis) and Droughtmaster cattle (Bos indicus x B. taurus), fitted with gastrointestinal cannulae, were dosed intrar uminally with fenbendazole at 7.5 mg/kg liveweight, together with a ch romium oxide capsule and a pulse dose of NaCoEDTA, to estimate the flo w dynamics of the digesta in the rumen and duodenum. The concentration s of fenbendazole (FBZ) metabolites were measured in plasma and duoden al fluid collected over 120 h. In plasma, significantly lower peak con centrations and earlier disappearance of FBZ and its sulphoxide (OFZ) metabolite were observed in buffalo, which considerably reduced system ic availability in comparison with cattle. The availability of OFZ in the duodenal fluid of buffalo was significantly lower, whereas FBZ dis position was similar to that in cattle. The turnover rate of fluid in the rumen was higher in buffalo than in cattle, while the flow paramet ers for other digesta were similar in the two species. It is concluded that the decreased absorption of drug in buffalo was attributable to the shorter residence time of the dose in the rumen, and probably in t he entire gastrointestinal tract. This may reduce the efficacy of trea tment and indicate the need for higher dose rates for benzimidazole an thelmintics in buffalo than in cattle.