Pharmacokinetics of ivermectin in the yak ( Bos grunniens)

The yak ( Bos grunniens) belongs to the cattle family Bovidae and lives in the mountains of China and adjacent areas. Due to the physiological adaptations of yak to its environment and the lack of data, the ivermectin pharmacokinetic was studied following a single subcutaneous dose at the recommended dose for cattle (0.2 mg kg −1). The observed peak plasma concentration ( C max) was 48.93 ng ml −1 and the time to reach C max ( T max) was 0.73 day. These results show a faster rate of absorption than in cattle. The values for the absorption half-life ( t 1/2a), the distribution half-life ( t 1/2 α ) and the terminal half-life ( t 1/2 β ) were 0.31, 0.74 and 4.82 days, respectively. The calculated area under the concentration–time curve (AUC) was 146.2 ng day ml −1 and the mean residence time (MRT) was 3.57 days. The availability of ivermectin appears low in yaks in comparison to cattle but equivalent to that reported in horses and is likely to be due to physiological characteristics of this species.