Cetrorelix

In plain language

Cetrorelix is a fertility drug, sold as Cetrotide, given as a daily small injection under the skin during IVF treatment. Its job is to prevent the ovaries from releasing eggs too early.

It blocks the brain's GnRH switch directly, so the body's own LH surge cannot fire before doctors are ready to retrieve the eggs. This lets clinics schedule the egg retrieval precisely and improve the timing of fertilization.

For students

Cetrorelix is a decapeptide GnRH antagonist (about 1,431 Da) with three D-amino acid substitutions and several non-standard residues, including D-citrulline at position 6. Direct receptor blockade suppresses LH within hours without the initial flare of agonists, a decisive practical advantage in IVF.

Administered daily by subcutaneous injection (0.25 mg) or as a single 3 mg dose with 4-day coverage during ovarian stimulation, it prevents premature LH surges. It is combined with gonadotropins in controlled ovarian stimulation protocols, and the antagonist protocol is now the dominant IVF approach worldwide because it is shorter, uses less medication, and carries a lower ovarian hyperstimulation risk than the classic long agonist protocol.

For researchers and instructors

Biochemistry. Third-generation GnRH antagonists solved the anaphylactoid histamine-release problem of earlier antagonists by substituting arginines with less cationic residues; cetrorelix's net design balances potency with a tolerability margin.

Pharmacology. Immediate suppression of LH (onset within 1-2 hours for 3 mg dose); no flare; rapid reversibility on discontinuation, an advantage when stimulation must be adjusted mid-cycle.

Human evidence. Pivotal trials established prevention of premature LH surges and comparable or better pregnancy rates versus agonist long protocols, with lower OHSS rates in meta-analyses.

Teaching point. The cleanest example in the series of antagonist-versus-agonist strategy: blocking a switch cleanly beats exhausting it when speed and reversibility matter.