Mechanism of Action
Competitive GnRH Receptor Blockade
Cetrorelix competitively occupies GnRH receptors on pituitary gonadotrophs, preventing natural GnRH binding and immediate suppression of LH and FSH release. The onset is rapid (within 4-8 hours), providing reliable LH surge prevention. Unlike GnRH agonists, there is no initial flare (transient LH/FSH rise) because cetrorelix blocks rather than activates the receptor. Suppression is fully reversible upon discontinuation.
IVF Antagonist Protocol
In IVF, ovarian stimulation with FSH/LH begins on cycle day 2-3. Cetrorelix is added when a lead follicle reaches 13-14 mm diameter (flexible start) or on day 5-6 (fixed start), continuing until the day of hCG/kisspeptin trigger. This antagonist protocol is shorter and more patient-friendly than the long agonist protocol while achieving equivalent IVF outcomes in most patient populations.
Research Summary
IVF Efficacy
FDA ApprovedMeta-analyses of GnRH antagonist vs agonist protocols in IVF show equivalent live birth rates overall. Antagonist protocols demonstrate superior patient outcomes in poor responders and reduced OHSS risk. OHSS risk is substantially lower because antagonist protocols allow GnRH agonist trigger instead of hCG in high-risk patients, virtually eliminating severe OHSS.
Prostate Cancer (off-label research)
Research InterestShort-term cetrorelix studied for prostate cancer testosterone suppression. Unlike degarelix (FDA-approved GnRH antagonist for prostate cancer), cetrorelix is primarily used in ART. Some data on cardiovascular safety advantages of GnRH antagonists vs agonists for prostate cancer patients with existing CV disease.
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Research Protocols
| Goal | Dose | Frequency | Route |
|---|---|---|---|
| IVF LH surge prevention (single dose) | 3 mg SC when lead follicle reaches 14 mm; if hCG not given within 4 days, add 0.25 mg/day until trigger | Single dose (then daily if needed) | Subcutaneous |
| IVF LH surge prevention (multiple dose) | 0.25 mg SC daily starting day 5-6 of stimulation or when lead follicle 13-14 mm | Daily until hCG trigger day | Subcutaneous |
Administer morning or evening consistently. Trigger oocyte maturation with hCG or GnRH agonist 36 hours before planned retrieval. Rotate injection sites.
Interactions
Safety Profile
Common: injection site reactions (redness, swelling, itching in ~10% of patients), nausea, headache. Ovarian hyperstimulation syndrome risk is lower than with GnRH agonist protocols, especially when GnRH agonist trigger used instead of hCG. Congenital anomaly rate in IVF is similar to spontaneous conception rates, not elevated by cetrorelix. Anaphylactoid reactions are rare but documented; patients should be observed for 30 minutes after first injection. Contraindicated in hypersensitivity to GnRH, mannitol, or cetrorelix components, and in severe renal impairment.
References
- [1]Al-Inany HG, et al. GnRH antagonists are safer than agonists. Cochrane Database Syst Rev. 2011;(5):CD006922.
- [2]Ludwig M, et al. Prevention of ovarian hyperstimulation syndrome by cetrorelix. Eur J Obstet Gynecol Reprod Biol. 2000;93(2):167-173.