Plasma levels and pharmacokinetics of ethynyl estrogens in various populations I. Ethynylestradiol

Single oral doses of ethynylestradiol (EE) ranging from 35 to 100 μg were given to a total of 98 adult women in Nigeria, Singapore, Sri Lanka, Thailand and the USA. Plasma levels of free EE were determined by radioimmunoassay and the appropriate pharmacokinetic parameters calculated. In two groups of USA women, one tested twice with the 35 μg dose and the other tested twice with the 100 μg dose, the within-subject coefficient of variation was 52 and 14%, and the between-subject coefficient of variation was 119 and 37%, emphasizing the importance of precise-and detailed experimental protocols. Substantial differences were observed in the kinetics of EE in the various localities; the origin of these differences, which might have considerable clinical significance, remains to be identified.