Cetrorelix (Cetrotide)

Cetrorelix (Cetrotide®) is a GnRH antagonist used in IVF to suppress LH surge and prevent premature ovulation. It is given as a daily 0.25 mg subcutaneous injection (or a single 3 mg dose) starting mid-stimulation until trigger day. It provides rapid, reversible suppression, has a good safety profile, and reduces the risk of OHSS, making it a cornerstone in modern IVF protocols.

What is Cetrorelix?

• Cetrorelix acetate is a GnRH antagonist.

• Brand name: Cetrotide®.

• Used in assisted reproductive technology (ART), particularly IVF, to prevent premature LH surge and ovulation.

Mechanism of Action

• Normally, GnRH from the hypothalamus stimulates the pituitary to release FSH & LH.

• Cetrorelix competitively binds to GnRH receptors in the pituitary → blocks GnRH action.

• This causes immediate suppression of LH and FSH secretion.

• Prevents premature ovulation, allowing controlled follicle growth with gonadotropins until retrieval.

Formulation & Dosage

Cetrorelix is supplied as pre-filled syringes or vials of lyophilized powder (reconstituted before use).

• Subcutaneous injection (usually in the lower abdomen).

Typical IVF use:

• 0.25 mg daily protocol →

  • Start when leading follicle is 12–14 mm (around day 5–6 of gonadotropin stimulation).

  • Continue daily until the day of trigger injection (hCG or GnRH agonist).

• Single-dose (3 mg protocol) →

  • One injection of 3 mg, which suppresses LH for about 4 days.

  • If stimulation continues beyond that, 0.25 mg daily injections are resumed.

Timing in IVF Cycle

1. Ovarian stimulation begins with gonadotropins (FSH ± LH).

2. Once follicles reach ~12–14 mm, Cetrorelix is started.

3. Continue until final oocyte maturation trigger is given.

4. Prevents LH surge and premature ovulation, so retrieval can be scheduled safely.

Benefits of Cetrorelix in IVF

• Immediate suppression (no flare effect like GnRH agonists).

• Shorter treatment duration vs. agonist long protocols.

• Lower risk of OHSS (ovarian hyperstimulation syndrome), especially if combined with GnRH agonist trigger instead of hCG.

• Convenient daily dosing.

Side Effects

Most are mild and self-limiting:

• Local: redness, itching, or swelling at injection site.

• General: headache, abdominal pain, nausea, mild ovarian cyst formation.

• Rare: hypersensitivity or allergic reaction.

• Very rare: severe anaphylactic reaction (contraindicated in patients with history of severe allergy).

Contraindications

• Pregnancy & lactation (not used outside IVF protocols).

• Hypersensitivity to cetrorelix, GnRH, or similar peptides.

• Severe kidney disease.

Clinical Notes

• Widely used in antagonist IVF protocols.

• Especially valuable for women at high risk of OHSS (young, high AMH, PCOS) because it allows use of a GnRH agonist trigger, which drastically reduces OHSS risk.

• Compared to Ganirelix, its clinical efficacy is similar; choice often depends on clinic preference and availability.