Pharmacokinetics of abamectin in sheep, goat and deer

Previous studies and anecdotal reports have generally suggested that goats and deer have higher metabolic rates of anthelmintics as compared to sheep. If this is correct then these animals are effectively under dosed if treated with the sheep dose rate. Underdosing is an accepted risk factor for developing anthelmintic resistance as it allows resistant, and even some partly resistant parasites to survive. Despite this risk, there has been no study to date, which has quantified the pharmacokinetic profile of abamectin in sheep, goats and deer rates under similar conditions. The objective of this research was to compare the pharmacokinetic parameters of interest esp. Cmax, Tmax and AUC in sheep, goats and deer given 0.2 mg/kg abamectin per os and then manipulate the dose rate for any variation to match that of sheep. The blood samples obtained from these animals were analysed by HPLC-Fluorescence detector using a validated method of analysis. Goats at the same dose rate had significantly lower Cmax (11.5 ± 1.6 ng/mL) as compared to sheep (20.1 ± 7.3 ng/mL) and deer (26.4 ± 7.0 ng/mL) with the latter two not being different to each other. Goats dosed with a double oral dose of abamectin (0.4 mg/kg) achieved a Cmax (20.2 ± 5.69 ng/mL) which was similar sheep and deer orally dosed with 0.2 mg/kg abamectin. The results of this study suggest that goats are being potentially underdosed at the sheep dose rates and efficacy studies of abamectin should be conducted in goats at both the dosing regimens. In contrast, these results do not support the hypothesis that deer are metabolising abamectin more rapidly than sheep and hence this dose rate would seem to be appropriate for deer but should be confirmed by further study.