Vaginal absorption of two estriol preparations

Abstract

In a comparative randomized cross-over study, the absorption of a single dose of 0.5 mg estriol from a vaginal cream or a vaginal suppository (Ovestin, Organon) was studied. Eight healthy postmenopausal women participated and the preparations were given with an interval of 14 days. Blood sampling was performed twice before application and then after 1/4, 1/2, 1, 2, 4, 6, 8, 24 and 48 h. Serum was analyzed for unconjugated and conjugated estriol (E3), FSH and LH [luteinizing hormone] by radioimmunoassay. Considerable interindividual variations in serum levels of unconjugated E3 were found but mean values were about equal throughout the study for the 2 preparations. Peak levels of 0.5-0.6 nmol/l were achieved 1-2 h after application of the preparations and after 24 h no unconjugated E3 was measurable. Conjugated E3 rose rapidly but within 48 h serum concentrations reached baseline levels. A maximum decrease in serum LH levels of .apprx. 40% was obtained with both preparations after 6 h and the return to baseline within 24 h indicates a relationship unconjugated E3. FSH in serum was maximally suppressed 6-12%. Estriol is thus readily absorbed by the vaginal route and peak levels of unconjugated E3 after insertion of 0.5 mg estriol seem to be comparable to those obtained after 8-12 mg estriol given orally.