At a glance

What is cetrorelix?

Cetrorelix is a synthetic peptide made of ten amino acids that acts as a GnRH antagonist, a drug that blocks the receptor for gonadotropin-releasing hormone in the pituitary gland. Its FDA-approved form is sold as Cetrotide¹ and is used during in vitro fertilization (IVF).

It is given as a small subcutaneous (under-the-skin) injection, usually in the abdomen, during the stimulation phase of an IVF cycle. Its job is narrow and practical: to keep the body from ovulating too early so that the growing eggs can be retrieved at the right time.

The history of cetrorelix

Cetrorelix came out of a long effort to improve how IVF controls ovulation. For years the standard approach used GnRH agonists, drugs that first overstimulate the pituitary and then, after about two weeks, exhaust and quiet it. That worked, but it was slow and caused an initial hormone "flare" and estrogen-withdrawal side effects. Researchers wanted a drug that would switch the signal off directly and immediately.

GnRH antagonists were the answer, and cetrorelix was among the first to reach the clinic for fertility care. The FDA approved¹ Cetrotide in 2000, giving IVF a shorter, simpler way to prevent premature ovulation. The antagonist approach has since become a mainstream option for ovarian stimulation.

How does cetrorelix work?

Cetrorelix works by blocking the pituitary receptor that normally triggers ovulation. Gonadotropin-releasing hormone is released in pulses from the hypothalamus and tells the pituitary to secrete luteinizing hormone (LH) and follicle-stimulating hormone (FSH). During IVF, as stimulated follicles grow and estrogen climbs, the body can launch a premature LH surge that makes the ovaries release their eggs too early and ruins the cycle. Cetrorelix is a decapeptide² that competes with natural GnRH for its receptor and occupies it, which rapidly suppresses LH and FSH release.

The key difference from GnRH agonists is timing:

That is why cetrorelix can be started later in the stimulation cycle and used for only a few days. It is given as a 0.25 mg dose injected daily. A single 3 mg dose was also studied, but only the 0.25 mg product is sold in the U.S.

The effect is reliable. According to PubMed, in a multicenter randomized trial a single 3 mg dose³ of cetrorelix prevented an LH surge in every patient studied, with shorter stimulation and fewer gonadotropin ampules than the long agonist protocol.

Is it FDA-approved?

Yes. The FDA approved¹ cetrorelix (Cetrotide) in 2000 for the inhibition of premature LH surges in women undergoing controlled ovarian stimulation. It is a prescription product used under the supervision of a fertility specialist, and it is approved specifically for this fertility use rather than as a general hormone treatment.

What is cetrorelix prescribed for?

Cetrorelix is prescribed to prevent premature ovulation during an IVF cycle. After a woman begins gonadotropin injections to grow multiple follicles, cetrorelix is added to hold back the LH surge until the eggs are mature, at which point a separate trigger shot is given and the eggs are retrieved. It is not a fertility drug in the sense of stimulating egg growth; it is the brake that keeps the timing under the clinic's control. It is contraindicated in:

• Pregnancy
• Women with severe kidney impairment
• Women with known hypersensitivity to the drug or to other GnRH analogs

Cetrorelix is used only within a monitored treatment cycle.

What are the side effects?

The most common effects are mild and local. They include:

• Injection-site reactions such as redness, itching, or swelling
• Nausea
• Headache

Serious effects are uncommon but worth knowing:

• Ovarian hyperstimulation syndrome (OHSS), a risk of the overall IVF stimulation; according to PubMed, a Cochrane review⁴ found that antagonist protocols reduced OHSS compared with the long agonist protocol, with no conclusive difference in live birth rate
• Allergic or hypersensitivity reactions, which can rarely be severe

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