Comparative Pharmacokinetics of Levamisole in Pregnant and Non-Pregnant Ewes: A Longitudinal Study

The influence of the state of pregnancy (days 45, 90, and 135 of gestation) on the pharmacokinetics of levamisole was investigated in ewes. Twelve healthy Merino female sheep were allocated into two groups (n = 6 per group). The ewes in group 1 (non-pregnant) were not mated, while the ewes in group 2 (pregnant) were mated with rams by synchronizing their estrus cycles. Levamisole was injected intramuscularly once at a dose of 7.5 mg/kg into all ewes. Blood samples were taken at 13 different times over a 48-h period according to a defined protocol. Plasma samples were analyzed for levamisole via high-performance liquid chromatography. Pregnant ewes had significantly lower C_max, AUC_0-last, and t_1/2ʎz of levamisole than non-pregnant ewes. There were no significant differences in T_max between the two groups. The values of AUC_0-last, C_max, and t_1/2ʎz decreased as pregnancy progressed. These results indicated that pregnancy reduced exposure (AUC_0-last) and duration of levamisole presence in the body. This information contributes to the use of levamisole in pregnant ewes, but further studies are needed to determine the change in therapeutic effect related to pregnancy.