Estrogenic preparations

Classification and main drugs

In clinical pharmacology, drugs interacting with estrogen receptors are typically divided into several key categories depending on their origin and mechanism of action.

1. Natural (native) estrogens. This group consists of hormones naturally present in the body. A classic example of a native hormone is estradiol.
2. Synthetic estrogens. Created chemically to intentionally alter pharmacological properties.
3. Ethinylestradiol is the most potent of all known synthetic estrogens. Its high pharmacological potency has made it the primary estrogenic component of the vast majority of combined oral contraceptives (COCs).
4. Mestranol is another synthetic drug that is essentially a prodrug. Upon entering the body, it undergoes metabolic conversion and transforms into active ethinylestradiol.
5. Selective estrogen receptor modulators. This group includes tamoxifen and clomifene. It is important to understand that they are not "pure" estrogens. Their uniqueness lies in their selectivity: in some target tissues they act as estrogens, while in others they exhibit strict antiestrogen activity.

Effect on the mammary gland and antiestrogen therapy

The mammary gland is a classic example of a strictly estrogen-dependent organ. This means its tissues are extremely sensitive to sex hormone levels.

• Tissue stimulation. Estrogens act as powerful stimulators of breast cell growth. Moreover, this stimulating effect is exerted not only by ovarian hormones, but also by estrogens synthesized in the body from precursors produced by the adrenal glands.
• Pharmacological intervention. In situations where hormonal stimulation of the mammary gland must be suppressed, drugs with antiestrogen action are used. A prominent representative is tamoxifen. Its mechanism of action involves binding to estrogen receptors directly within the glandular tissue and blocking them. Thus, the pathological link "estrogens $\rightarrow$ mammary gland" is disrupted, and the hormones lose their ability to stimulate the organ.

Pharmacological profile of tibolone

A special place in the physician's arsenal is held by tibolone, a drug with a complex mechanism of action. Like mestranol, tibolone is a prodrug. Its pharmacological effects manifest only after oral administration and subsequent metabolism.

During biotransformation, tibolone forms two different types of metabolites that provide a wide spectrum of activity:

1. Metabolites exhibiting estrogenic activity.
2. Metabolites combining progestogenic and androgenic activity.

Due to this combined action, tibolone has a major clinical advantage: it is successfully used for hormone replacement therapy (HRT) as monotherapy. Patients do not require additional administration of other estrogen drugs.

Clinical effects of the androgenic component: The presence of androgenic metabolites provides several additional positive effects:

• Significant improvement in overall well-being.
• Effective alleviation of vasomotor symptoms (relief of "hot flashes").
• Enhanced sexual desire (increased libido).

Breast safety profile: Tibolone has a high safety profile regarding the mammary gland, exerting an antiproliferative effect on it. The defense mechanism is implemented at the enzymatic level: the drug causes selective inhibition of the sulfatase enzyme in the breast tissue. Sulfatase blockade disrupts the desulfation of estrone. As a result of this cascade, the local formation of metabolically active estrone completely ceases.

Class and exam questions

What else to study on this topic

• Biosynthesis of estrogens from adrenal precursors.
• Pharmacokinetics and biotransformation stages of mestranol.
• Tissue specificity of selective modulators using clomifene as an example.
• Progestogenic activity of tibolone metabolites in monotherapy.

Other topics in the section "Hormone preparations, their synthetic substitutes, and antagonists"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.