Bioavailability of oestriol

Abstract

A rapid radioimmunoassay, using a specific antiserum against oestriol (Oe3) was developed for the analyses of unconjugated oestriol in post-menopausal women before and after oral administration of oestriol.One ml plasma was extracted once with 10 ml diethyl ether and assayed without further purification. The plasma levels of oestriol in post-menopausal women appear to be below 5 pg/ml. When 10 ml plasma from a pool was assayed 2.9 pg/ml was found. When 1 ml was assayed from individual patients levels between 10\p=n-\20 pg was found, which was not different from the plasma blank. A rise in plasma oestriol was found already 15 min after oral administration of 6 mg or 12 mg oestriol (Ovesterin\s=r\). On the average there was a plasma oestriol peak after 45 min and then a gradual decrease to low levels within 3 to 4 h. It is concluded that oestriol is rapidly absorbed when administered orally. However, the duration of the plasma oestriol elevation is short. Oestriol is rapidly metabolized. The short elevation probably explains the weak oestrogenic effect exerted by oestriol when administered once a day as receptor affinity for oestriol is low.

Use of lactobacilli and estriol combination in the treatment of disturbed vaginal ecosystem: a review

“…Unlike E2, after single-dose oral or vaginal applications of E3 in normal doses (oral: 8-10 mg; vaginal: 0.5 mg), there is no, or only a weak proliferative, effect on the endometrium (23). Estrogens administered vaginally are absorbed in a dosedependent, bypass hepatic metabolism and are biologically active (24,25). Vaginal estrogens are more effective in relieving urogenital symptoms than oral preparations as (1) lower doses are required due to the absence of hepatic metabolism, and (2) high local estrogen level induces direct vaginal response (2,26).…”

Treatment of vaginal atrophy with estriol and lactobacilli combination: a clinical review

“…After oral administration, E3 is readily absorbed and metabolized in the liver, so that only 1-2% of the administered dose reach the circulation in an unchanged active form. Following administration of 8 mg of E3, a maximum serum level of 75-220 pg/ml is reached after 1-3 hours 36,50 . Following vaginal application, about 20% of the dose reaches the circulation in an unchanged form.…”

“…However, only continuous vaginal use of high doses of 'potent' estrogens (like estradiol, E2) may have safety concerns as this effect is known to depend on hormone type, dose and frequency of administration 35 . Vaginally administered estrogens are absorbed in a dosedependent manner 36,37 . Vaginal estrogens are more effective in relieving urogenital symptoms than oral preparations because lower doses are required due to the absence of hepatic metabolism and high local estrogen concentrations 35,38 .…”

“…The endogenous daily production of E3 during the premenopause, calculated from the metabolic clearance rate and plasma concentration, is known to range around 14 ± 2 mg/day in the follicular phase and 23 ± 2 mg/day in the luteal phase. During the postmenopause, the mean value is 11 ± 4 mg/day 36,[44][45][46][47][48][49] . In serum, 8% of E3 is unbound and 92% is bound to transport proteins 50 .…”

Comparison of the effects of add-back therapy with various natural oestrogens on bone metabolism in rats administered a long-acting gonadotrophin-releasing hormone agonist

“…Oestriol would, therefore, be expected to be an appropriate oestrogen used for add-back therapy. The duration of plasma OE 3 elevation is 3-4 h after an oral administration (Englund et al 1982). Notably, OE 3 exerts either oestrogenically antagonistic or agonistic effects (Clark et al 1977, Heimer 1987, Melamed et al 1997.…”