Antagon, Fyremadel, Orgalutran
Evidence Grade A — Regulatory approved. 187 published studies. 104 registered clinical trials.
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Ganirelix (originally sold as Antagon) is an injectable medication used during IVF to prevent premature ovulation, ensuring eggs can be collected at the optimal time. It was the first GnRH antagonist approved in the US for fertility treatment and comes in a convenient prefilled syringe for daily self-injection. In clinical practice, it is considered interchangeable with cetrorelix.
187 published studies: 158 human, 8 animal, 62 in-vitro, 20 reviews
Ganirelix was originally marketed as Antagon (approved July 1999), making it the first GnRH antagonist approved in the US. It is indicated for prevention of premature LH surges during controlled ovarian stimulation, administered as a daily 250 mcg subcutaneous injection starting mid-cycle.
In clinical practice, ganirelix and cetrorelix are considered therapeutically equivalent, with fertility clinic preference often determined by practical factors such as prefilled syringe convenience, local availability, and cost. Both have been instrumental in the shift from longer GnRH agonist protocols to the shorter, safer antagonist protocols that now dominate IVF practice worldwide.
Ganirelix works identically to cetrorelix — it directly blocks the GnRH receptor in the pituitary gland to prevent the premature LH surge that would trigger ovulation before eggs are ready for collection during IVF. It provides immediate suppression of LH (approximately 74% reduction within four hours of injection) with rapid reversibility once stopped. The practical difference from cetrorelix is primarily in formulation: ganirelix comes as a ready-to-use prefilled syringe, while cetrorelix requires reconstitution.
Ganirelix and cetrorelix are clinically equivalent — no head-to-head trials have shown meaningful differences in pregnancy rates or safety between them. The choice is typically driven by formulary availability, cost, and practical factors like prefilled syringe convenience versus the need for reconstitution. Together, these two drugs helped shift IVF practice worldwide from longer GnRH agonist protocols to shorter antagonist protocols that reduce the risk of ovarian hyperstimulation syndrome and require fewer injections. Generic ganirelix has improved affordability and access. No major new research programmes are active for ganirelix specifically.
IVF Outcomes With Time-Lapse Culture: Comparison Between PPOS and GnRH Antagonist Protocols
Is the Diurnal Variation in Circulating Levels of Cortisol Reflected in Follicular Fluid of Preovulatory Follicles Close to Ovulation?
hCG Priming in Women With Diminished Ovarian Reserve
PPOS (Progestin Primed Ovarian Stimulation) and Corifollitropin Alfa (CFA) Cross-over Study
Disentangling the Effects of Daily Stress, Sleep, and Sex Hormones on Accelerated Vascular Aging in Midlife Women
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Histrelin is available as Supprelin LA for central precocious puberty (approved 2007). The Vantas implant for prostate cancer was approved in 2004 but discontinued in 2021. The implant requires a minor surgical procedure for insertion and removal/replacement each year. Supprelin LA's main clinical advantage is its 12-month duration — the longest of any GnRH agonist — which is particularly valuable in paediatric patients where treatment compliance over years is important. Clinical studies demonstrated effective suppression of puberty markers in over 97% of patients. The implant has also seen significant off-label use in gender-affirming care as a puberty blocker, where its annual dosing schedule offers practical benefits for adolescent patients and their families.
Goserelin is marketed as Zoladex by AstraZeneca, available as 3.6 mg monthly and 10.8 mg three-monthly subcutaneous implants. First approved in 1989, it is used in advanced prostate cancer, premenopausal breast cancer, endometriosis, and for thinning the uterine lining before surgical procedures. Goserelin achieves castrate-level testosterone suppression (below 50 ng/dL) within two to four weeks. Its unique implant delivery system means there is no liquid injection, reconstitution, or refrigeration required — a practical advantage in some clinical settings. Like all GnRH agonists, it causes an initial hormone flare before suppression takes effect. Goserelin holds an important niche in breast cancer treatment, where it is used to suppress ovarian function in premenopausal women with hormone-receptor-positive disease, often in combination with aromatase inhibitors.
Nafarelin is marketed as Synarel (approved 1990) for endometriosis and central precocious puberty. It requires administration as one spray in each nostril twice daily — a higher frequency than injectable alternatives but avoids needles entirely, which can be a significant advantage for some patients, particularly children. Clinical trials showed symptom improvement in 75–92% of endometriosis patients. However, absorption can be affected by nasal congestion or concurrent use of nasal decongestants, which can be a practical limitation. As with all GnRH agonists, prolonged use leads to bone density loss, and treatment for endometriosis is typically limited to six months. Nafarelin occupies a niche for patients who prefer non-injectable hormone suppression, though it has become less commonly prescribed as longer-acting depot injections and oral alternatives have become available.
