Nafarelin is not available for use by any other routes than intranasal administration. Side effects
Side effects of nafarelin are related to sex hormone deficiency and include hot flashes, vaginal dryness, headaches, mood changes, and sexual dysfunction. Nafarelin causes erectile dysfunction in more than half of men with benign prostatic hyperplasia treated with it. Some people may experience acne, muscle pain, reduced breast size, and nasal irritation. These side effects are reversible and should resolve after stopping the medication. There is a case report of severe hyperkalemia during nafarelin therapy in a woman with uterine fibroids. The mechanism is unknown. Pharmacology
Pharmacodynamics
Nafarelin is a GnRH agonist, or an agonist of the GnRH receptor, the biological target of GnRH. It works by continuously activating the GnRH receptor, which results in profound desensitization of the receptor such that it becomes non-functional. As a result, nafarelin suppresses the GnRH-induced secretion of the gonadotropins, luteinizing hormone and follicle-stimulating hormone, from the pituitary gland. This, in turn, results in profound suppression of gonadal sex hormone production, as well as reversible suppression of fertility. Pharmacokinetics
The bioavailability of nafarelin with intranasal administration is 2.8% on average, with a range of 1.2 to 5.6%. The plasma protein binding of nafarelin is 80%. It is metabolized primarily by peptidases and not by cytochrome P450 enzymes. The elimination half-life of nafarelin is 2.5 to 3.0 hours by intranasal administration, whereas the half-life of nafarelin and its metabolites by subcutaneous injection is 85.5 hours. Nafarelin is eliminated 44 to 55% in urine and 18.5 to 44.2% in feces.
It is effective in the treatment of benign prostatic hyperplasia. Dosages
Nafarelin is used to treat precocious puberty at a dosage of 1,600 to 1,800 μg per day. The 1,600 μg/day dosage is achieved by two sprays (400 μg total) into each nostril in the morning (four sprays, 800 μg total) and two sprays (400 μg total) into each nostril in the evening (four sprays, 800 μg total). If 1,600 μg/day is insufficient for adequate pubertal suppression, the 1,800 μg/day dosage can be used instead. This is achieved by three sprays (600 μg total) into alternating nostrils three times per day (nine sprays per day total). When administering the sprays, the head should be tilted back slightly and 30 seconds should elapse between each spray. A bottle of nafarelin nasal spray (brand name Synarel) lasts for about 7 days at a dosage of 1,600 μg/day.Nafarelin is used to treat endometriosis at lower dosages of 400 to 800 μg per day. This is achieved by one or two sprays (200 or 400 μg total) into alternating nostrils once in the morning and once in the evening (two to four sprays per day total). A bottle of nafarelin nasal spray (brand name Synarel) lasts for about 30 days at a dosage of 400 μg/day. Available forms
Nafarelin is available in the form of a 0.2% nasal spray for use one, two, or three times per day. Each bottle of nafarelin nasal spray (brand name Synarel) contains about 60 sprays delivering approximately 200 μg nafarelin in 100 μL solution per actuation.