Pharmacokinetics of ampicillin during pregnancy

Levels of ampicillin in plasma and urine were studied in 26 pregnant women during the 8 hr following an oral as well as an intravenous dose. Identical doses were given to the same women after pregnancy, and the resulting plasma and urine levels were compared. Assays were performed by means of a disk agar diffusion method. Renal plasma clearance was calculated. Plasma levels were significantly lower during pregnancy than after. The difference was unrelated to body weight and length of gestation but was associated with a significant increase in distribution volume and renal plasma clearance in pregnant women. Recovery of ampicillin in urine during 8 hr was identical during pregnancy and after. It is suggested that pregnant women require higher doses of ampicillin per kg of body weight than nonpregnant women in order to achieve similar concentrations in plasma. The experimental design used in the present study is suitable for evaluation of pharmacokinetics in pregnancy.