Nafarelin

What is Nafarelin?

Nafarelin (brand name SYNAREL) is a synthetic decapeptide GnRH (LHRH) agonist delivered via intranasal spray twice daily. It was approved by the FDA on February 16, 1990, and remains the only intranasal GnRH agonist available on the US market.

Approved indications:

• Endometriosis — for symptom management and lesion suppression in adults
• Central precocious puberty — for pubertal suppression in children

Structure and Mechanism

Nafarelin is identical to native GnRH except for substitution of D-2-naphthylalanine at position 6, conferring high receptor affinity and enzymatic resistance.

Pharmacologically:

• Like other GnRH agonists, continuous receptor activation produces pituitary desensitization
• LH and FSH secretion declines within 2-4 weeks
• In women: estradiol falls to postmenopausal levels, suppressing endometriotic lesion activity
• In children with CPP: gonadal steroidogenesis is suppressed, halting pubertal progression

The intranasal delivery is feasible because nafarelin's relative bioavailability (~3% via nasal mucosa) is sufficient to achieve therapeutic levels with practical dosing volumes.

Clinical Evidence

Endometriosis (Fertility and Sterility 1988-1990):

• Multiple Phase 3 trials in women with endometriosis
• Significant reductions in pelvic pain, dysmenorrhea, and dyspareunia at 6 months
• Comparable efficacy to danazol with better tolerability (no androgenic side effects)

Central precocious puberty:

• Effective hormonal suppression in pediatric CPP
• Improved predicted adult height
• Now generally supplanted by leuprolide depot or histrelin implant due to easier dosing for pediatric patients

Approval History

• February 16, 1990 — FDA approval (Synarel)
• 1992 — CPP indication added

Place in Therapy

Nafarelin's main current niche is endometriosis in patients who prefer or tolerate nasal administration over injections. It is dosed as one spray (200 µg) in alternating nostrils twice daily, with treatment limited to 6 months continuous due to bone mineral density concerns from prolonged hypoestrogenism.

In CPP, leuprolide depot and histrelin implant have largely supplanted nafarelin because nasal twice-daily dosing is impractical for chronic pediatric care.

Safety Profile

Adverse events from hypoestrogenism:

• Hot flashes (most common)
• Vaginal dryness, decreased libido
• Mood changes, headache
• Bone mineral density loss (limits chronic use to ~6 months)

Nasal-specific:

• Local nasal irritation, rhinitis
• Reduced absorption with concurrent nasal decongestants

Distinction from Other GnRH Agonists

Nafarelin's intranasal delivery distinguishes it from depot/implant GnRH agonists:

The patient self-administers nafarelin as a nasal spray, which can be a benefit (no injections, no clinic visits) or a problem (twice-daily adherence, nasal mucosa sensitivity).