SYNAREL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for SYNAREL (SYNAREL).
Synthetic decapeptide analog of gonadotropin-releasing hormone (GnRH). Binds to pituitary GnRH receptors, initially stimulating then desensitizing them, leading to suppressed LH and FSH secretion, decreased gonadal steroid production (estrogen, testosterone).
| Metabolism | Metabolized by peptidases in plasma and tissues (no specific CYP enzyme involvement). |
| Excretion | Renal: ~90% as parent drug and metabolites; fecal: <10%. |
| Half-life | Terminal elimination half-life: ~3 hours (range 2-5 hours) after intranasal administration; clinically, dosing every 12 hours maintains therapeutic levels. |
| Protein binding | ~70% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | Vd: ~1.1 L/kg (range 0.8-1.5 L/kg), indicating extensive distribution into total body water and tissues. |
| Bioavailability | Intranasal: ~5% (range 2-10%) relative to subcutaneous injection, due to limited nasal absorption and first-pass metabolism. |
| Onset of Action | Intranasal: suppression of gonadotropins within 2-4 hours; maximal suppression of LH and FSH occurs within 2-4 weeks of continuous therapy. |
| Duration of Action | Intranasal: serum levels decline below therapeutic threshold within 6-12 hours after a single dose; chronic therapy results in sustained pituitary desensitization lasting as long as treatment continues. |
200 mcg intranasally twice daily (400 mcg total daily dose) for 6 months. Initiate on day 5 of menstural cycle.
| Dosage form | SPRAY, METERED |
| Renal impairment | No specific dose adjustment provided for GFR-based modifications. Use with caution in severe renal impairment. |
| Liver impairment | No specific dose adjustment provided for Child-Pugh-based modifications. |
| Pediatric use | Not indicated for use in pediatric patients. |
| Geriatric use | Not indicated for use in geriatric patients; no specific dose adjustment available. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for SYNAREL (SYNAREL).
| Breastfeeding | Not recommended during breastfeeding. Excretion in human milk unknown; potential for serious adverse effects in nursing infant. M/P ratio not available. |
| Teratogenic Risk | FDA Pregnancy Category X. Contraindicated in pregnancy. Risk of fetal harm, including congenital malformations (e.g., craniofacial, CNS, cardiovascular defects) and pregnancy loss, particularly during first trimester due to gonadotropin suppression and hormonal alterations. Avoid use in pregnant women. |
| Fetal Monitoring |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to GnRH or any component","Undiagnosed abnormal vaginal bleeding","Pregnancy or potential pregnancy (teratogenic)","Breastfeeding","Use in endometriosis beyond 6 months (off-label extension not recommended)"]
| Precautions | ["Rapid symptom improvement does not rule out malignancy; evaluate if no response within 4 weeks.","Bone mineral density loss with prolonged use; consider risk-benefit for conditions requiring >6 months therapy.","Hypersensitivity reactions including anaphylaxis have been reported.","May cause ovarian cyst enlargement in initial weeks; monitor with ultrasound if pelvic pain occurs.","Cannot be used in children with precocious puberty until bone age confirmed."] |
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| Pregnancy test before initiating therapy; confirm non-pregnant status. Monitor for signs of pregnancy loss or fetal anomalies if exposure occurs. Ultrasonography for fetal assessment if inadvertent use during pregnancy. |
| Fertility Effects | Inhibits gonadotropin secretion, leading to suppressed ovulation and spermatogenesis, causing reversible infertility. Return to fertility typically after discontinuation. |