Effect of pregnancy on plasma phenobarbital concentrations in rats.

We examined the pharmacokinetics of phenobarbital before and during pregnancy in rats. Animals were divided into four groups: (a) control, (b) pregnant, (c) phenobarbital-treated, and (d) phenobarbital-treated pregnant groups. The increase in body weight of nonpregnant or pregnant rats was not influenced by long-term phenobarbital treatment. Plasma phenobarbital concentrations during the period of long-term phenobarbital treatment with a fixed dosage by body weight were not significantly affected by pregnancy. Furthermore, pregnancy did not affect pharmacokinetic parameters of phenobarbital between 0.25 and 24h after administration. These results suggest that pregnancy does not influence on the pharmacokinetics of long-term phenobarbital treatment at a fixed dosage by body weight.