For treatment of central precocious puberty (true precocious puberty, GnRH-dependent precocious precocity, complete isosexual precocity) in children of both sexes and for the treatment of endometriosis.
Nafarelin is a potent agonistic analog of gonadotropin-releasing hormone (GnRH). At the onset of administration, nafarelin stimulates the release of the pituitary gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), resulting in a temporary increase of gonadal steroidogenesis. Repeated dosing abolishes the stimulatory effect on the pituitary gland. Twice daily administration leads to decreased secretion of gonadal steroids by about 4 weeks; consequently, tissues and functions that depend on gonadal steroids for their maintenance become quiescent. After nafarelin therapy is discontinued, pituitary and ovarian function normalize and estradiol serum concentrations increase to pretreatment levels. Recurrences of endometriosis are frequent after cessation of any hormonal therapy, or surgery that leaves the ovaries and/or uterus intact.
Mode of Action:
Like GnRH, initial or intermittent administration of nafarelin stimulates release of the gonadotropins luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland, which in turn transiently increases production of estradiol in females and testosterone in both sexes. However, with continuous daily administration, nafarelin continuously occupies the GnRH receptor, leading to a reversible down-regulation of the GnRH receptors in the pituitary gland and desensitization of the pituitary gonadotropes. This causes a significant and sustained decline in the production of LH and FSH. A decline in gonadotropin production and release causes a dramatic reversible decrease in synthesis of estradiol, progesterone, and testosterone by the ovaries or testes. Like normal endometrium, endometriotic implants contain estrogen receptors. Estrogen stimulates the growth of endometrium. Use of nafarelin induces anovulation and amenorrhea and decreases serum concentrations of estradiol to the postmenopausal range, which induces atrophy of endometriotic implants. However, nafarelin does not abolish the underlying pathophysiology of endometriosis. In children with central precocious puberty receiving nafarelin, serum LH, testosterone, and estradiol concentrations return to prepubertal levels. This results in the supression of secondary sexual characteristics and decrased rate of linear growth and skeletal maturation. Following disconinuation of nafarelin, the effects of the drug is reversed, meaning FSH and LH concentrations usually return to pretreatment levels.
In experimental animals, a single subcutaneous administration of up to 60 times the recommended human dose (on a µg/kg basis, not adjusted for bioavailability) had no adverse effects. At present, there is no clinical evidence of adverse effects following overdosage of GnRH analogs.
Hugues JN, Cedrin Durnerin IC: Revisiting gonadotrophin-releasing hormone agonist protocols and management of poor ovarian responses to gonadotrophins. Hum Reprod Update. 1998 Jan-Feb;4(1):83-101. Pubmed Garner C: Uses of GnRH agonists. J Obstet Gynecol Neonatal Nurs. 1994 Sep;23(7):563-70. Pubmed Henzl MR: Gonadotropin-releasing hormone analogs: update on new findings. Am J Obstet Gynecol. 1992 Feb;166(2):757-61. Pubmed Burry KA: Nafarelin in the management of endometriosis: quality of life assessment. Am J Obstet Gynecol. 1992 Feb;166(2):735-9. Pubmed Saltiel E, Garabedian-Ruffalo SM: Pharmacologic management of endometriosis. Clin Pharm. 1991 Jul;10(7):518-31. Pubmed Chrisp P, Goa KL: Nafarelin. A review of its pharmacodynamic and pharmacokinetic properties, and clinical potential in sex hormone-related conditions. Drugs. 1990 Apr;39(4):523-51. Pubmed Letassy NA, Thompson DF, Britton ML, Suda RR Sr: Nafarelin acetate: a gonadotropin-releasing hormone agonist for the treatment of endometriosis. DICP. 1990 Dec;24(12):1204-9. Pubmed
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