The comparative serum disposition kinetics of subcutaneous administration of doramectin, ivermectin and moxidectin in the Australian Merino sheep.

This study evaluates the comparative serum disposition kinetics of injectable formulations of doramectin (DRM), ivermectin (IVM) and moxidectin (MXD) in Australian Merino sheep. Thirty-six, 2-year-old sheep were allocated by weight into six groups of six animals. Animals in each group received 200 microg/kg of DRM, MXD, IVM or a combination of two of these drugs by subcutaneous (s.c.) injection. Blood was collected at designated intervals (between 1 h and 40 days after treatment) and the serum analysed by high performance liquid chromatography (HPLC) using fluorescence detection. The results indicated that MXD administration produced a significantly higher maximum serum concentration and a more rapid absorption as compared with DRM and IVM. MXD and DRM had a significantly larger area under the concentration vs. time curve (AUC) than IVM, suggesting a more persistent effect for the former two products in sheep. The AUC for DRM was significantly higher when administered alone as compared with that observed when given in combination with MXD or IVM, suggesting preferential elimination of DRM compared with IVM and MXD from concurrent s.c. administration.