GnRH antagonist · IVF cycles
Cetrorelix is a synthetic decapeptide based on gonadotropin-releasing hormone (GnRH), with amino acids changed at five positions so that it blocks the GnRH receptor instead of activating it. It is used in IVF and related fertility treatment to stop the body from releasing eggs too early while the ovaries are being stimulated.
Two pituitary hormones, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), drive the ovaries, and their release is controlled by GnRH from the hypothalamus. Mid-cycle, rising estradiol triggers a surge of LH that causes ovulation. During ovarian stimulation, an early surge can release eggs before they are retrieved. Cetrorelix competes with natural GnRH for receptors on pituitary cells and suppresses LH release within hours, with a stronger effect on LH than on FSH1. Because it is an antagonist, it does not produce the initial release of gonadotropins seen with GnRH agonists, and its effects on LH and FSH reverse after treatment stops1. Because it acts quickly, it can be started partway through stimulation, avoiding the long suppression phase that agonist protocols need3.
In a French multicenter randomized study, a single cetrorelix injection in the late follicular phase prevented premature LH surges in all 115 women who received it; compared with a long-acting GnRH agonist, stimulation was shorter and ovarian hyperstimulation less frequent, fewer eggs were collected, and pregnancy rates were not statistically different2.
A 2016 Cochrane review of 73 randomized trials (12,212 women) compared GnRH antagonists as a class with long GnRH-agonist protocols in IVF and ICSI. It found no clear difference in live birth but a lower rate of ovarian hyperstimulation syndrome with antagonists, rated as moderate-quality evidence3. A long-acting form of cetrorelix was also studied in men with symptomatic benign prostatic hyperplasia, where a dose-ranging trial reported improved urinary symptom scores4; that use has not been approved.
FDA approved cetrorelix as Cetrotide in 2000 to inhibit premature LH surges in women undergoing controlled ovarian stimulation1,5; generic versions have since been approved.
In clinical studies of 949 women, reported events included moderate or severe ovarian hyperstimulation syndrome (3.5%), nausea and headache, along with mild, short-lived injection-site redness, bruising, itching or swelling1. Allergic reactions, including anaphylactoid reactions with the first dose, have been reported after approval1. It is contraindicated in known or suspected pregnancy, during breastfeeding, in severe kidney impairment, and in people allergic to GnRH analogs or mannitol1.
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