Comparative pharmacokinetic behaviour of albendazole in sheep and goats

Albendazole (ABZ) containing a trace of [14C]-ABZ was administered intraruminally at 4.75 mg kg-1 to Merino sheep and Angora goats and the pharmacokinetic behaviour of ABZ and its metabolites in plasma nd abomasal fluid compared. The systemic availability (area under the curve, AUC) for total [14C]-labelled metabolites was significantly lower in goats than in sheep. This was largely attributable to the disposition of ABZ sulphoxide (ABZ.SO) which had a significantly lower maximum concentration (Cmax) in goats (0.94 +/- 0.04 micrograms ml-1) than in sheep (1.41 +/- 0.24 micrograms ml-1). The AUC of [14C] in abomasal fluid was similar in goats and sheep, with approximately 35 and 45% of the dose passing the pylorus in the two species, respectively. ABZ, ABZ.SO and ABZ sulphone (ABZ.SO2) were present in the abomasal fluid of both species but between-species differences were only evident with ABZ.SO which had a lower Cmax in goats compared with sheep. The relative proportions of the [14C] dose excreted in urine and faeces were similar between species. It is suggested that ABZ may be sequestered to a greater extent in the liver of goats than of sheep which would result in lower concentrations of ABZ.SO in plasma and abomasal fluid. This behaviour might be compensated for by administering ABZ to goats at a proportionally higher dose rate.