Influence of lactation on plasma phenobarbital concentrations in rats.

The effect of lactation on the pharmacokinetics of phenobarbital (PB) after delivery was studied in female rats. Non-pregnant animals received PB 20 mg/kg/day twice for 6-7 days before mating, during pregnancy and after delivery. Chronic PB did not significantly influence changes in the body weight of rats after delivery. On the first post-delivery day, the plasma PB concentration in the PB-treated rats was significantly higher than that in PB-treated, non-pregnant rats (non-pregnant rats); and thereafter, it gradually decreased until ablactation on the 20th day. After ablactation, plasma PB concentrations gradually returned to the level before delivery. In PB-treated rats, pharmacokinetic parameters (Cmax, AUC0-12) of PB between 0 and 12 hr after a single oral administration were significantly decreased during lactation. These results suggest that PB administered during lactation is transferred in part to offspring through maternal milk.