Pharmacokinetics of fenoterol in pregnant and nonpregnant women.

The pharmacokinetics of the beta 2-adrenergic drug fenoterol, which is used as a tocolytic agent in pregnancy, has been investigated in pregnant (n = 9) and nonpregnant (n = 5) women during a constant rate intravenous infusion. Clearance and mean residence time were found to be 1990 (1879/2220; Median, Q25/Q75) ml/min and 9.2 (8.0/14.0) min in the pregnant and 2126 (1915/2130) ml/min and 16.6 (16.5/32.1) min in the nonpregnant women, respectively. In addition, fenoterol clearance was estimated in 88 women from a single blood sample collected at steady state during IV therapy and the effect of gestational age on clearance was studied. Clearance displayed large interindividual variation. There was no apparent correlation between clearance and gestational age. We conclude that there is no need to adjust the dose on pharmacokinetic grounds in the course of pregnancy.