Estriol Other names: Oestriol

Estriol is a natural female hormone. Unlike other estrogens, estriol is short acting. It substitutes for the loss of estrogen production.

In cases of vaginal atrophy, vaginally administered estriol induces normalisation of the vaginal epithelium and thus helps to restore the normal microflora and a physiological pH in the vagina.

Treatment of vaginal estrogen deficiency symptoms: Vaginally applied estrogen alleviates the symptoms of vaginal atrophy due to estrogen deficiency in postmenopausal women.

Absorption

After administration of estriol vaginal cream, estriol is also absorbed from the vagina into the general circulation, shown by a sharp rise in plasma estriol, followed by a gradual decline.

Distribution

Peak plasma levels are reached 1-2 hours after application. After vaginal application of 0.5 mg estriol, C_max is approximately 100 pg/ml, C_min is approximately 25 pg/ml and Caverage is approximately 70 pg/ml. After 3 weeks of daily administration of 0.5 mg vaginal estriol, Caverage has decreased to 40 pg/ml.

In a clinical trial, median plasma levels measured 12 hours after administration following 12 weeks of estriol vaginal cream administration were 8.5 pg/ml. Following a median of 21 months (IQR, 9.2-38.4) of trice weekly administration, median serum oestriol levels in chronic group was 5.5 pg/ml (IQR, 1.9-10.2).

Biotransformation

Nearly all (90%) estriol is bound to albumin in the plasma and, in contrast with other estrogens, hardly any estriol is bound to sex hormone-binding globulin. The metabolism of estriol consists principally of conjugation and deconjugation during the enterohepatic circulation.

Elimination

Estriol, being a metabolic end product, is mainly excreted via the urine in the conjugated form. Only a small part (±2%) is excreted via the feces, mainly as unconjugated estriol.

No particulars.