GnRH antagonist · IVF cycle control
Ganirelix is a synthetic ten-amino-acid peptide that blocks the pituitary's receptor for gonadotropin-releasing hormone (GnRH). In fertility treatment it is used to prevent a premature surge of luteinizing hormone (LH) while the ovaries are being stimulated, so eggs can be retrieved at the planned time. It was first approved in the US as Antagon.
GnRH from the hypothalamus drives the pituitary to make LH and follicle-stimulating hormone (FSH). Around mid-cycle, a large rise in GnRH triggers an LH surge that sets off ovulation. During IVF the ovaries are stimulated to grow several follicles, and an early LH surge could release eggs before they are collected. Ganirelix competitively occupies GnRH receptors on pituitary cells, producing a rapid, reversible drop in gonadotropin release, with LH suppressed more than FSH. Because it is an antagonist, no initial burst of gonadotropin release has been detected, and suppression starts quickly. After it is stopped, pituitary LH and FSH recover within about 48 hours2.
Approval rested on randomized human trials in women undergoing controlled ovarian stimulation. A phase 3 trial in North America randomized 313 women to either a ganirelix protocol or a long leuprolide protocol. Ganirelix yielded slightly fewer eggs on average (11.6 versus 14.1), with similar fertilization rates and numerically lower ongoing pregnancy rates per attempt (30.8 versus 36.4 percent); moderate injection-site reactions were reported about half as often (about 12 versus 24 percent), and treatment courses were shorter with fewer injections1. Across the label's controlled trials in 794 treated women, the events recorded most often, counted regardless of cause, were gynecological abdominal pain, fetal death (pregnancy loss), headache, ovarian hyperstimulation syndrome and vaginal bleeding2.
An observational study of more than 1,000 newborns found congenital anomaly rates after ganirelix cycles comparable with those after GnRH-agonist cycles2.
The FDA approved ganirelix in 1999, originally as Antagon, to inhibit premature LH surges in women undergoing controlled ovarian hyperstimulation2,4,5; generic versions are also approved. It is authorised in the European Union as Orgalutran3.
In the controlled trials, the events recorded most often, regardless of cause, were gynecological abdominal pain, fetal death (pregnancy loss), headache, ovarian hyperstimulation syndrome, vaginal bleeding, injection-site reactions and nausea. Allergic reactions, including anaphylaxis, angioedema and hives, have been reported after approval, sometimes with the first injection. It is contraindicated in known or suspected pregnancy and in people allergic to GnRH or its analogs, and the label says it should be prescribed by physicians experienced in infertility treatment2.
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