Anthelmintic efficacy, plasma and milk kinetics of eprinomectin following topical and subcutaneous administration to yaks (Bos grumniens)

Eprinomectin is recommended for use as an anti-parasitic agent in livestock, including cattle. Yaks are a member of the cattle family living in the high altitude mountains of China and adjacent countries; however, there have been no clinical trials of the anthelmintic efficacy and pharmacokinetics of eprinomectin in yaks. The purpose of this study was to investigate the endectocidal efficacy and pharmacokinetics of eprinomectin following topical (at 0.5 mg/kg) and subcutaneous (at 0.2 mg/kg) administration in the yak. After topical administration, plasma eprinomectin reached a peak value of 15.31 ± 3.71 ng/ml (Cmax) at 3.01 ± 1.22 days (Tmax). In milk, the Cmax was 3.74 ± 1.05 ng/ml at 3.00 ± 0.88 days. The AUC0-t for plasma was 193.84 ± 26.34 ng d/ml and for milk AUC0-t was 46.24 ± 10.37 ng d/ml. The mean residence time (MRT) was 10.74 ± 1.44 days and 10.90 ± 3.87 days in plasma and milk, respectively. After subcutaneous administration, the Cmax was 35.78 ± 10.53 ng/ml at 0.91 ± 0.39 days in plasma and 9.10 ± 3.61 ng/ml at 1.61 ± 1.05 days in milk. The MRTs in plasma and milk were 3.07 ± 1.50 and 3.64 ± 1.15 days, respectively. The AUC0-t was 133.71 ± 32.51 ng d/ml for plasma and 43.85 ± 14.16 ng d/ml for milk. Both the pour-on and injectable formulation of eprinomectin were similarly efficacious (minimum egg count reductions of 94% and 96.4%, respectively) at each post-treatment time point. However, Tmax, MRT and t1/2el were longer, and Cmax of eprinomectin in the plasma and milk were lower, following topical administration compared to those after subcutaneous administration. In conclusion, these results support the use of eprinomectin in yaks. The pour-on formulation of eprinomectin can be recommended for nematode control in lactating yaks with no milk-withdrawal period because of its low residue profile and good efficacy.