Comparative clinical pharmacological aspects of oral and transdermal dosage forms of estrogens

• Evgenia V. Shikh

Abstract

Hormone replacement therapy (HRT) is commonly used to treat a range of conditions characterised by estrogen deficiency. HRT can effectively reduce the symptoms of estrogen deficiency, treat urogenital atrophy successfully, prevent osteoporosis. In medical practice estrogens can be administered orally or via the vaginal or transdermal route. The most optimal is a transdermal route, in which the active ingredient goes directly into the systemic circulation.

When estrogen is administered orally, there is the first-pass effect through the liver, whereas transdermal administration avoids first-pass metabolism in the liver, which results in a higher bioavailability and, in some cases, higher safety. Concentration of estrone - estrogen metabolite - which causes a number of side effects, is lower with transdermal estrogen.

Despite the differences in the processes of absorption, distribution and excretion between oral and trans­dermal estrogen, dose of 17β-estradiol 1 mg gel and 2 mg (1 dragee) of estradiol valerate may be considered equivalent in terms of efficacy, as confirmed in a number of comparative clinical studies.

The risks of estrogen hormone replacement therapy can be minimized by proper choice of the dose and route of administration (dosage forms) in estrogen-deficient states.

Keywords:estrogens, route of administration, bioavailability, safety

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