Cetrorelix

Cetrorelix is a synthetic decapeptide that functions as a gonadotropin-releasing hormone (GnRH) receptor antagonist. By binding competitively to pituitary GnRH receptors, it prevents the GnRH-induced release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). This suppression of the LH surge helps prevent premature ovulation during controlled ovarian stimulation, a key component of assisted reproductive technologies such as in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). It is used in IVF/ICSI cycles and in some donor oocyte cycles, and in certain protocols as an alternative to GnRH agonists, often contributing to lower OHSS risk and shorter treatment courses.

Cetrorelix is administered by subcutaneous injection. In typical IVF protocols, it is started during the follicular phase, commonly when the lead follicle reaches about 12–14 mm, and given as 0.25 mg daily, though regimens may vary. The antagonist is continued through the stimulation period and is usually discontinued at the time of the ovulation trigger (with human chorionic gonadotropin or, in some regimens, a GnRH agonist) to permit final follicular maturation.

Pharmacologically, cetrorelix acts rapidly and has a short duration of action, producing suppression of LH within hours without the initial stimulatory flare associated with GnRH agonists. It is generally well tolerated; common adverse effects include injection-site reactions, headache, nausea, and hot flashes. Rare hypersensitivity reactions can occur. Contraindications include hypersensitivity to cetrorelix or its components and pregnancy.