Pharmacokinetics of intravenous theophylline in pregnant patients at term.

The pharmacokinetics of theophylline was determined in six pregnant, nonsmoking women in labor at term following a single bolus infusion of 5.6 mg/kg of aminophylline over 20 minutes. Cord blood levels were obtained from three babies at delivery. Compared to values reported in the literature for nonpregnant adult nonsmokers, the volume distribution (mean 573 +/- 53 ml/kg) and clearance rate (mean .88 +/- .24 ml/kg/min) of theophylline is increased in pregnant women, but the half-life (mean 7.95 +/- 2 hrs) remains unaltered. Similar doses of aminophylline can therefore be used in pregnant and nonpregnant adults who do not smoke cigarettes, but the infusion rate required to maintain a mean serum concentration of 10 micrograms/ml (0.5 mg/kg/hr) is almost half that initially reported in the literature. The serum theophylline concentrations in maternal venous and mixed cord blood at delivery were almost identical, which implies that theophylline crosses the placenta rapidly and that the fetus represents a "shallow" drug compartment.