Description

Lynestrenol is a synthetic progestogen (progestin) belonging to the 19-nortestosterone group. It is an oral medication that serves as a prodrug; it is rapidly converted in the body to its pharmacologically active metabolite, Norethisterone. Lynestrenol is used for a wide range of gynecological and reproductive health purposes, primarily to treat conditions associated with hormonal imbalances.

Indication

Lynestrenol is indicated for the treatment of various gynecological conditions where a progestational effect is desired. Its main indications include:

• Contraception: As a progestin-only oral contraceptive (the “mini-pill”).

• Abnormal Uterine Bleeding: To treat dysfunctional uterine bleeding (menorrhagia) by stabilizing the uterine lining.
• Endometriosis: To manage the pain and other symptoms of endometriosis by suppressing the growth of endometrial tissue outside the uterus.

• Amenorrhea: To induce withdrawal bleeding in women with a lack of menstruation.

• Polymenorrhea: To regulate menstrual cycles characterized by abnormally frequent periods.

• Hormone Replacement Therapy (HRT): In combination with an estrogen, it is used in postmenopausal women with an intact uterus to prevent endometrial hyperplasia and reduce the risk of endometrial cancer.

Mechanism of Action

The therapeutic effects of Lynestrenol are not due to the drug itself but are mediated through its active metabolite, Norethisterone, which acts as a potent agonist at progesterone receptors.

1. Metabolic Conversion: After oral administration, Lynestrenol is quickly and extensively metabolized in the liver to its active form, Norethisterone.
2. Progesterone Receptor Agonism: Norethisterone then binds with high affinity to progesterone receptors in the hypothalamus, pituitary gland, and reproductive organs (uterus, cervix, etc.). This binding initiates a series of physiological responses that are characteristic of progesterone.

3. Suppression of Ovulation (Contraceptive Effect): By acting on the hypothalamus and pituitary, Norethisterone inhibits the release of gonadotropin-releasing hormone (GnRH), which in turn suppresses the secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). The suppression of the LH surge is crucial for preventing ovulation.
4. Endometrial Effects: Norethisterone causes the endometrium (the uterine lining) to become thin, atrophic, and unsuitable for the implantation of a fertilized egg. This action is key for treating abnormal bleeding and is a component of its contraceptive effect. In endometriosis, this action helps to suppress the growth of the ectopic endometrial tissue.
5. Cervical Mucus Alteration: It causes the cervical mucus to become thick and viscous, creating a barrier that is difficult for sperm to penetrate.

The therapeutic effects of Lynestrenol are essentially the same as those of its active metabolite, Norethisterone.