What is nafarelin, and how does it work (mechanism of action)?
Nafarelin is a synthetic (man-made) protein that blocks the effects of the natural gonadotropin-releasing hormone (GnRH), a hormone that regulates the output of gonadotropins (a class of hormones) by the pituitary gland (a small gland located at the base of the brain). Gonadotropins (follicle stimulating hormone or FSH and luteinizing hormone or LH) are hormones that cause estrogen production by the ovaries. When nafarelin (known scientifically as a GnRH analog) is administered continuously to women in their reproductive years, the pituitary output of FSH, LH, and the production of estrogen by the ovaries are suppressed. Suppression of estrogen production causes menstruation to stop, resulting in a temporary (but reversible) state of "menopause." This temporary state of menopause results in shrinkage of the lining of the uterus, known as the endometrium.
Endometriosis is a condition whereby the cells that normally form the endometrium inside of the uterus are instead found outside of the uterus. These abnormally located cells (called endometrial implants) are most commonly found on the ovaries, Fallopian tubes, outer surfaces of the uterus or intestines, and on the surface lining of the pelvic cavity. Like the normal endometrium, implants respond to the hormones of the menstrual cycle, i.e., they build up during the month, then break down and bleed during menstruation. However, unlike normal endometrium, the implants bleed internally. (blood from implants cannot exit the body like blood from the uterus can.) The internal bleeding, followed by tissue inflammation and subsequent scarring, is believed to be responsible for the symptoms of pain and infertility in women with endometriosis. Nafarelin has been found to be effective in relieving the pain of endometriosis and shrinking the endometrial implants.
FSH and LH also control the onset of puberty in boys and girls. Therefore, administration of nafarelin blocks the puberty-promoting effects of FSH and LH, reducing the development of secondary sexual characteristics (such as pubic hair) and skeletal development in boys and girls with abnormally early puberty (central precocious puberty) due to problems in the brain that result in high levels of FSH and LH. The FDA approved nafarelin in February 1991.
What brand names are available for nafarelin?
Synarel
Is nafarelin available as a generic drug?
GENERIC AVAILABLE: No
Do I need a prescription for nafarelin?
Yes
What are the uses for nafarelin?
Nafarelin is prescribed for the management of endometriosis pain and decreasing the size of endometrial implants. Nafarelin is also used for the treatment of central precocious puberty.
What are the side effects of nafarelin?
Side effects of nafarelin are mostly related to the low estrogen state. Common side effects include:
- hot flashes,
- vaginal dryness,
- headaches,
- mood changes, and
- decreased interest in sex.
Other important side effects include:
- acne,
- muscle pain,
- reduced breast size, and
- irritation of the tissue inside the nose.
These side effects should disappear after stopping the medication.
The low estrogen state and the temporary menopause induced by nafarelin can cause a small amount of bone thinning, which may only partially recover after stopping treatment. Patients should discuss this possibility with their doctors and alert their doctors to conditions that they may have that could increase the risk of bone thinning. These conditions include chronic tobacco use, excessive use of alcohol, family history of osteoporosis, and taking other medications that can cause bone thinning (such as anticonvulsants or corticosteroids).
What is the dosage for nafarelin?
For treatment of endometriosis nafarelin is given as one spray (200 µg) into one nostril in the morning and one spray in the other nostril in the evening for 6 months. The first dose of nafarelin should be taken between the second and fourth day after menstrual bleeding begins. After the first two months of nafarelin treatment, most women can expect a decrease in menstrual flow, and menstruation may stop altogether. For women who continue to experience normal menstrual cycles after two months of treatment, the daily dose may be increased to 800 µg daily.
Central precocious puberty is treated with 1600-1800 µg daily administered as four sprays in alternating nostrils twice daily or three sprays in alternating nostrils three times daily. Thirty seconds should elapse between sprays.
For optimal effectiveness and safety, nafarelin has to be given continuously without interruption. Missing one or more doses can cause vaginal bleeding. Missing successive doses can cause release of an egg from the ovary (ovulation) and result in pregnancy, unless proper contraceptive measures have been followed. Since birth control pills cannot be used with nafarelin, it is important to use non-hormonal methods of contraception (such as a diaphragm with contraceptive jelly, IUD, or condoms) while taking nafarelin.
Absorption of nafarelin is not affected by a cold or runny nose. If nasal decongestant sprays are needed, they should be taken at least 2 hours before or after using nafarelin.
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Which drugs or supplements interact with nafarelin?
Nasal decongestant sprays (for example, Afrin) may interfere with the absorption of nafarelin. If nasal decongestant sprays are needed, they should be used at least 2 hours before or after using nafarelin.
Is nafarelin safe to take if I’m pregnant or breastfeeding?
Nafarelin should not be used in pregnancy or in women who may become pregnant while receiving the medication because it might harm the fetus. Safe use of nafarelin in pregnancy has not been established. Pregnancy must be excluded before starting treatment with this medication, and a non-hormonal method of contraception should be used during treatment.
Nafarelin should not be used by nursing mothers because its safety has not been evaluated.
What else should I know about nafarelin?
What preparations of nafarelin are available?
Nasal spray: 200µg/spray
How should I keep nafarelin stored?
Nafarelin should be stored at room temperature, 15 to 30 C (59 to 86 F).