Cetrorelix

Overview

GnRH antagonists differ from GnRH agonists (like leuprolide or triptorelin) in that they suppress gonadotropins immediately, without the initial "flare" of hormone release. Cetrorelix occupies pituitary GnRH receptors competitively, so its effect is rapid in onset and quickly reversible once dosing stops.

In IVF, cetrorelix is added during the late follicular phase of ovarian stimulation to block a premature LH surge that would otherwise trigger early ovulation and compromise egg retrieval. The randomized trial by Olivennes and colleagues showed that cetrorelix achieved surge prevention with outcomes comparable to a long GnRH-agonist protocol while shortening treatment duration and reducing the number of injections, helping establish the modern "antagonist protocol." Cetrorelix has also been studied in benign prostatic hyperplasia and endometriosis.

It is generally well tolerated; the most common effects are injection-site reactions and, in stimulation cycles, symptoms related to the underlying ovarian hyperstimulation.

Mechanism of Action

By antagonizing GnRH receptors on gonadotroph cells, cetrorelix rapidly lowers circulating LH and FSH in a dose-dependent, reversible manner. Because it does not first stimulate the receptor, there is no flare effect, so it can be introduced later in the stimulation cycle and stopped promptly, allowing a shorter and more flexible protocol. Restoration of normal gonadotropin secretion occurs quickly after discontinuation.

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