Placental Transfer of Albendazole Sulphoxide Enantiomers in Sheep

Albendazole sulphoxide (ABZSO) is an anthelmintic drug used in veterinary practice. Its molecule has a chiral centre in the sulphur atom and racemic formulations are always used. The kinetics of the ABZSO enantiomers in the last third of pregnancy in ewes, and the placental transfer to the fetus, were studied after a single-dose oral administration (7.5 mg/kg) of a racemic formulation. In mothers, the area under the plasma concentration-time curve (AUC) and Cmax values of (+)-ABZSO (42.4±10.5 μg/mL and 1.9±0.4 μg/mL, respectively) were higher than those of (−)-ABZSO (15.3±5.1 μg/mL and 1.0±0.3 μg/mL). The MRT values were 17.0±1.6 h for (+)-ABZSO and 13.1±1.8 h for (−)-ABZSO. Similar kinetic parameters were obtained in the fetus for both enantiomers, but the fetal concentrations were lower compared with values for the dam. The AUC ratio between (−)-ABZSO/(+)-ABZSO in the dam was 0.36 and in the fetuses 0.64, indicating a higher impairment for the (+)-enantiomer in its placental transfer to the fetus.