Paracetamol pharmacokinetics during the first trimester of human pregnancy.

Paracetamol pharmacokinetics was evaluated in groups of pregnant (8-12 weeks) and non pregnant women given the standard oral dose of 650 mg. The mean half-life was significantly lower and oral clearance was significantly higher in the first trimester group compared to the control group. The AUC was lower in the first trimester but the difference was not significant. The maximum serum concentration (Cmax) was reached 48 min after administration in both groups, and the mean maximal serum concentration was similar in the pregnant and non-pregnant women (11.16 and 11.58 micrograms.ml-1). A correlation of r = 0.85 was found between Cmax and the weight of the pregnant women (P < 0.01) but not with the weight of the control women, this suggests that weight gain might be used to determine the women in whom dosage adjustment is needed.