Short answer: Cetrotide (cetrorelix) and ganirelix are both GnRH antagonists given once a day under the skin during IVF stimulation to stop early ovulation.12 Cetrotide 0.25 mg is mixed from powder and kept in the fridge; ganirelix 250 mcg comes in a prefilled syringe kept at room temperature. Neither label reports a trial against the other.
| Cetrotide (cetrorelix) | Ganirelix | |
|---|---|---|
| Approved for | Preventing early LH surges (early ovulation) in women having controlled ovarian stimulation1 | Preventing early LH surges in women having controlled ovarian hyperstimulation2 |
| Form | 0.25 mg powder vial mixed with a prefilled syringe of sterile water; used right away1 | 250 mcg in 0.5 mL prefilled syringe2 |
| Label dosing | 0.25 mg once a day from stimulation day 5 (morning or evening) or day 6 (morning) until the hCG day1 | 250 mcg once a day in the mid to late follicular phase until the hCG day; trials started on day 6 of FSH2 |
| Days used in trials | Median 5 days (range 1 to 15)1 | Mean 5.4 days (range 2 to 14)2 |
| Storage | Fridge, 2 to 8 C (36 to 46 F), in the carton1 | Room temperature, 25 C (77 F), protected from light2 |
| Side effects at 1% or more | Moderate or severe OHSS 3.5%, nausea 1.3%, headache 1.1% (949 women)1 | Gynecological belly pain 4.8%, pregnancy loss 3.7%, headache 3.0%, OHSS 2.4% (794 women)2 |
| Boxed warning | None1 | None2 |
| Missed dose | No rule in the label1 | No rule in the label2 |
Yes, both block the GnRH receptor so the pituitary does not release an early LH surge while FSH or hMG grows the follicles. The Cetrotide label says LH suppression starts about two hours after a 0.25 mg dose and a dose every 24 hours keeps it going.1 The ganirelix label says steady levels are reached after 3 days and LH and FSH fully recover within 48 hours of stopping.2
The ganirelix label also notes that because ganirelix works with the body's own FSH, the FSH dose given by injection may be lowered.2
Neither label has a placebo group, and both count events from the first dose until pregnancy was confirmed, without regard to cause. That is why ganirelix's table lists pregnancy loss (3.7%): it is a count of what happened during the cycle, not a measured drug effect.2 Cetrotide's table lists moderate or severe OHSS (3.5%), nausea (1.3%) and headache (1.1%), and the label says injection site redness, bruising, itching and swelling were usually mild and brief.1 These numbers come from separate trials with different people, lengths and methods, so they are not a head-to-head comparison.
Both labels warn about allergic reactions, including with the first dose, reported after approval.12
Which one fits a cycle is your fertility team's call. More detail: Cetrotide side effects, ganirelix side effects, and the Cetrotide and ganirelix dosing schedules.