Pharmacological properties : תכונות פרמקולוגיות

Pharmacodynamic Properties

5.1   Pharmacodynamic properties
Pharmacotherapeutic group: natural and semisynthetic estrogens
ATC code: G03CA04
Estriol: The active ingredient, synthetic estriol, is chemically and biologically identical to human estriol. It substitutes for the loss of estrogen production in menopausal women, and alleviates atrophic vaginitis.

Ovestin Cream contains the synthetic hormone estriol. In the years just before and after the menopause (whether naturally or surgically induced) estriol can be used in the treatment of urogenital symptoms and complaints related to estrogen deficiency. In cases of vaginal atrophy estriol induces normalisation of the vaginal epithelium and thus helps to restore the normal microflora and a physiological pH in the vagina. As a result it increases the resistance of the vaginal epithelial cells to infection and inflammation.

Estriol is relatively short-acting estrogen due to its short nuclear retention time in endometrial cells, its low affinity for plasma proteins and partly as a result of this, its rapid metabolic clearance. Endometrial proliferation is not expected when estriol is given in a single daily dose, since this requires sustained, occupancy of the nuclear estrogen receptor. As a consequence, undesired vaginal bleeding rarely occurs during treatment with estriol and an increased risk of endometrial carcinoma is unlikely.

Relief of urogenital symptoms was achieved during the first weeks of treatment.

Pharmacokinetic Properties

5.2   Pharmacokinetic properties
After administration of Ovestin 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.

After 3 weeks of administration of a single daily dose, a similar absorption pattern to that seen for a single application was observed.

Daily treatment with 0.5 mg of estriol (in 0.5 g of cream) leads to a sharp rise in unconjugated plasma estriol levels to 110 pg/ml at one hour from previously undetectable levels (<12 pg/ml). This was followed by a gradual decline during the next 5 hours to around 60 pg/ml.


On day 21 of treatment, mean baseline estriol levels of about 26 pg/ml rose to a mean peak value of 95 pg/ml at 1 hour. A decline similar to that seen on day 1 was observed during the next 5 hours.

Vaginal administration permits the absorption of the active (unconjugated, or free) form of estriol into the blood for transport to the target tissues, prior to its inactivation via conjugation by enterohepatic enzymes.