Abstract

The plasma kinetic profile of ivermectin during the last trimester of pregnancy was studied in ewes after a single subcutaneous administration of 0.2 mg/kg body weight (BW). Sheep were randomly distributed into two groups. Ewes in group 1 (control, n = 6) were left unmated, whereas in group 2 (pregnant, n = 6) ewes were estrus-synchronized and mated with rams. Both groups were housed under similar conditions of management and feeding. At 120 days of pregnancy, both groups were given a subcutaneous injection of 0.2 mg/kg BW of ivermectin. Blood samples were taken by jugular puncture according to a fixed protocol between 1 h and 40 days post-treatment. After plasma extraction and derivatization, samples were analyzed by high performance liquid chromatography with fluorescence detection. A computerized pharmacokinetic analysis was performed, and the data were compared by means of the Student t-test. The results showed that plasma concentrations of ivermectin remained longer in the pregnant than in the control group. The mean values of pharmacokinetic parameters C max, t max, and area under the concentration-time curve (AUC) were similar for both groups of sheep. The mean residence time (MRT) values for the pregnant group (8.8 ± 1.4 days) were higher (P < 0.05) than those observed in the control group (5.3 ± 1.9 days). It can be concluded that pregnancy increases the residence time of ivermectin in the plasma of pregnant sheep when it is administered subcutaneously. © 2007 The Authors.