Plasma oestriol following vaginal administration: morning versus evening insertion and influence of food.

The aim of this trial was to study the vaginal absorption of oestriol and to investigate whether morning rather than evening oestriol administration would produce different plasma oestriol patterns. The influence of food intake on plasma oestriol levels was also investigated. Nine post-menopausal women were given 0.5 mg oestriol (ovula supplied by Leo AB, Sweden) intravaginally every evening for 16 days. Thereafter, 1 mg oestriol was given every evening for another 5 days, except on treatment days 18 and 19 when 1 mg oestriol was given in the morning instead. Venous blood samples were collected at frequent intervals on day 19 (morning administration) and a meal was allowed 4 h later. On the day 21 (evening administration), venous blood samples were taken at frequent intervals during the night and no meal was given until the next morning. Plasma concentrations of unconjugated oestriol were measured by means of a specific radioimmunoassay (RIA). A difference was seen in the plasma oestriol patterns when the results following morning and evening administration were compared. However, no significant difference as regards the total 24-h systemic availability of oestriol was observed. A minimal increase in plasma oestriol levels was seen after a meal in the case of both morning and evening intravaginal oestriol administration, possibly as a result of enterohepatic recirculation.