Cetrorelix

Cetrotide

Cetrorelix is a synthetic decapeptide analog of gonadotropin-releasing hormone (GnRH) engineered as a receptor antagonist. It is built with several non-natural amino-acid substitutions that let it bind the pituitary GnRH receptor and block it competitively, without activating it. This produces an immediate, dose-dependent fall in luteinizing hormone (LH) and follicle-stimulating hormone (FSH) — the opposite of GnRH agonists like leuprolide or triptorelin, which first cause a surge ('flare') before eventually suppressing the axis through receptor downregulation. That immediacy is exactly why cetrorelix is valuable in assisted reproduction. During controlled ovarian stimulation for in vitro fertilization (IVF), the goal is to grow multiple follicles with injected gonadotropins while preventing the body from triggering its own premature LH surge, which would release the eggs before they can be collected. Cetrorelix, given during the stimulation phase, provides rapid and reversible blockade of the LH surge without a flare, allowing a shorter, more flexible protocol than the older long agonist protocols. Its effect wears off quickly after stopping, so the pituitary recovers promptly. Cetrorelix is given by subcutaneous injection and was approved by the FDA (Cetrotide) for the prevention of premature ovulation in women undergoing controlled ovarian stimulation. The GnRH-antagonist approach it represents has become a mainstay of modern IVF because it allows the use of a GnRH-agonist 'trigger' to mature the eggs, which markedly reduces the risk of ovarian hyperstimulation syndrome compared with older methods. It is generally well tolerated, with mild injection-site reactions being the most common complaint. It is a prescription fertility medicine used within a supervised IVF cycle.