Pharmacokinetics of oral 17 beta-estradiol.

The pharmacokinetics of oral 17 beta-estradiol (E2) were evaluated: only a limited amount of information is available on the subject. Because of the first passage hepatic effect, the blood levels of estrone (E1) are greater than those of E2; similar profiles exist for oral E1 sulfate, micronized E2 and E2 valerate. However, the short-term effects of oral E2 versus E1 on hepatic parameters may vary somewhat. Peak levels of E1 and E2 are achieved four hours after the administration of 1 mg of E2 and average 200 and 40-50 pg/mL, respectively. A dose-response relationship exists for serum levels achieved after oral E2 administration. Twelve-hour values are representative of the 24-hour profile. With prolonged use, the 24-hour levels may be equally representative and serum E2 levels increase, suggesting some cumulative effects. Smoking enhances the hepatic metabolism of oral estrogen and results primarily in a lower unbound E2 level.