Vaginal absorption of two estriol preparations

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 (OvestinR, Organon, The Netherlands) 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 hours. Serum was analysed for unconjugated and conjugated estriol (E3), FSH and LH by radio-immunoassay. Considerable interindividual variations in serum levels of unconjugated E3 were found but mean values were about equal throughout the study for the two preparations. Peak levels of 0.5-0.6 nmol/l were achieved 1-2 hours after application of the preparations and after 24 hours no unconjugated E3 was measurable. Conjugated E3 rose rapidly but within 48 hours serum concentrations reached baseline levels. A maximum decrease in serum LH levels of about 40% was obtained with both preparations after 6 hours and the return to baseline within 24 hours indicates a relationship to 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.