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A class of drugs that block the effects of progesterone

Overview

Antiprogestogens are a class of drugs that inhibit the effects of progesterone, a key hormone involved in the menstrual cycle, pregnancy, and embryogenesis. These compounds act by blocking the progesterone receptor, thereby preventing progesterone from exerting its biological effects. Antiprogestogens are used in various clinical settings, including contraception, abortion, and the treatment of certain cancers.

Mechanism of Action

Antiprogestogens function by binding to the progesterone receptor, which is a type of nuclear receptor. By occupying the receptor, these drugs prevent progesterone from binding and activating the receptor, thus inhibiting the transcription of progesterone-responsive genes. This blockade can lead to changes in the endometrium, inhibition of ovulation, and disruption of pregnancy.

Clinical Uses

Contraception

Antiprogestogens can be used as a form of emergency contraception. By preventing the action of progesterone, these drugs can inhibit or delay ovulation, thereby reducing the likelihood of fertilization and implantation.

Medical Abortion

One of the most well-known uses of antiprogestogens is in medical abortion. The drug mifepristone, also known as RU-486, is commonly used in combination with a prostaglandin analogue to terminate early pregnancy. Mifepristone works by causing the decidual breakdown, leading to detachment of the blastocyst and increased uterine contractility.

Cancer Treatment

Antiprogestogens have potential applications in the treatment of progesterone receptor-positive breast cancer and endometrial cancer. By blocking progesterone, these drugs can inhibit the growth of hormone-dependent tumors.

Examples of Antiprogestogens

Mifepristone

Mifepristone is the most widely used antiprogestogen. It is used for medical abortion, emergency contraception, and in some cases, for the treatment of Cushing's syndrome.

Ulipristal Acetate

Ulipristal acetate is another antiprogestogen used for emergency contraception and the treatment of uterine fibroids. It acts as a selective progesterone receptor modulator (SPRM), exhibiting both agonistic and antagonistic effects depending on the tissue.

Side Effects

The use of antiprogestogens can lead to various side effects, including nausea, vomiting, abdominal pain, and vaginal bleeding. Long-term use may also affect bone density and menstrual cycle regularity.

Related Pages

• Progesterone
• Contraception
• Medical abortion
• Breast cancer

Gallery

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