The pharmacokinetics of moxidectin after oral and subcutaneous administration to sheep

The pharmacokinetic parameters of moxidectin were determined in ten sheep following a single subcutaneous or oral drench at a dose of 0.2 mg.kg(-1). The plasma kinetics were best fitted by a two-compartment model. Moxidectin was detected in the plasma at the first sampling time (1 h) and thereafter for at least 60 d. The AUC were similar after both treatments indicating the same bioavailability for the two routes of administration. The oral route was characterized by a higher Cmax value (28.07 ng.mL(-1)) than after subcutaneous injection (8.29 ng.mL(-1)) and by significantly faster absorption as indicated by Tmax of 0.22 d and 0.88 d for oral and subcutaneous administrations, respectively. The most striking result of this experiment was the longer mean residence time reported for the subcutaneous route, i.e. 16.80 d as compared to 12.55 d for the oral drench. This difference is in agreement with previous studies demonstrating the longer anthelmintic efficacy of the subcutaneous route in comparison with oral administration. (C) Inra/Elsevier, Paris.