Nafarelin

Nafarelin is a synthetic GnRH agonist decapeptide administered as a nasal spray, approved by the FDA under the brand name Synarel. It is indicated for management of endometriosis and central precocious puberty. Nafarelin is approximately 200 times more potent than endogenous GnRH and produces medical hypogonadism through pituitary desensitization. Its intranasal route offers a needle-free alternative to injectable GnRH analogs.

Nafarelin binds with high affinity to pituitary GnRH receptors, initially stimulating LH and FSH release. With twice-daily intranasal administration, continuous non-pulsatile receptor occupancy desensitizes pituitary gonadotrophs and downregulates GnRH receptor density. Within approximately 4 weeks, LH and FSH secretion falls substantially, reducing ovarian estradiol production to postmenopausal levels. This estrogen deprivation induces atrophy of endometriotic implants and relieves the pain and dysmenorrhea characteristic of endometriosis. In central precocious puberty, suppression of the hypothalamic-pituitary-gonadal axis halts premature puberty progression. Effects are fully reversible after stopping treatment.

Randomized trials demonstrate nafarelin 400 mcg/day equivalent to danazol for endometriosis pain relief, with a more favorable androgenic side effect profile. Approximately 80% of patients report significant improvement in dysmenorrhea, pelvic pain, and dyspareunia after 6 months of treatment. Bone mineral density decreases by 3–5% during 6-month treatment, typically recovering within 6–12 months post-treatment. For central precocious puberty, nafarelin 1600–1800 mcg/day suppresses pubertal hormones and decelerates bone age advancement, preserving final adult height. Long-term follow-up data confirm normal fertility after treatment discontinuation.