Pharmacokinetics of single and multiple doses of ethinyl estradiol and levonorgestrel in relation to smoking

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Abstract
The effects of tobacco and oral contraceptive (OC) use (Ovral) on the pharmacokinetics of levonorgestrel (0.25 mg) and ethinyl estradiol (50 .mu.g) were examined. Young women (n = 27) were grouped as follows: I: non-OC users/nonsmokers; II: OC users/nonsmokers; III: non-OC users/smokers; and IV: OC users/smokers. The apparent clearance of levonorgestrel in group I was 80.9 .+-. 15.6 ml/hr/kg and the half-life was 19.3 hours. A significant decrease in levonorgesterel clearance was seen in the chronic OC users (groups II and IV). The apparent oral clearance of ethinyl estradiol was 1002 .+-. 398 ml/hr/kg in group I and the half-life averaged 7.7 hours. Groups II and III showed decreased (not significant) clearances of ethinyl estradiol. Tobacco use had no effect on steroid pharmacokinetics in the non-OC users. Although chronic OC use did not affect ethinyl estradiol clearance, a joint effect of tobacco/OC use on enhancing clearance of ethinyl estradiol appeared to occur. A linear relationship was found between 24-hour trough serum concentrations and AUC values of both steroids that may facilitate population monitoring studies of OC exposure.