Name: Antagon

What is Antagon (ganirelix)?

Ganirelix is a man-made form of a protein that reduces the amount of certain hormones in the body, including estrogen.

Ganirelix is used along with other medications to regulate hormones during treatment for infertility in women.

Ganirelix may also be used for purposes not listed in this medication guide.

What is the most important information I should know about Antagon (ganirelix)?

You should not use this medication if you are allergic to ganirelix or similar medications such as leuprolide (Lupron, Eligard), goserelin (Zoladex), or nafarelin (Synarel).

Before using ganirelix, tell your doctor if you are allergic to latex rubber.

Do not use ganirelix if you are already pregnant. Your doctor may give you a pregnancy test to make sure you are not pregnant before you receive ganirelix.

You should not breast-feed while you are being treated with ganirelix.

During your treatment with ganirelix, your blood may need to be tested often. Visit your doctor regularly. You must remain under the care of your doctor while using ganirelix.

Some women using this medicine have developed a condition called ovarian hyperstimulation syndrome (OHSS), especially after the first treatment cycle. OHSS can be a life-threatening condition. Call your doctor right away if you have any of the following symptoms of OHSS: severe pelvic or stomach pain, swelling or weight gain, shortness of breath, diarrhea, nausea, vomiting, or urinating less than usual.

Antagon (ganirelix) side effects

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Some women using this medicine have developed a condition called ovarian hyperstimulation syndrome (OHSS), especially after the first treatment cycle. OHSS can be a life-threatening condition. Call your doctor right away if you have any of the following symptoms of OHSS:

  • severe pelvic pain;

  • swelling of the hands or legs;

  • stomach pain and swelling;

  • shortness of breath;

  • weight gain;

  • diarrhea;

  • nausea or vomiting; or

  • urinating less than usual.

Less serious side effects may include:

  • pelvic pain (similar to menstrual cramps);

  • mild nausea or stomach pain;

  • headache;

  • vaginal bleeding; or

  • pain, redness, or irritation at the injection site.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Commonly used brand name(s)

In the U.S.

  • Antagon

Available Dosage Forms:

  • Solution

Therapeutic Class: Endocrine-Metabolic Agent

Pharmacologic Class: Luteinizing Hormone Releasing Hormone Antagonist

Proper Use of Antagon

To make using ganirelix as safe and reliable as possible, you should understand how and when to use this medicine and what effects may be expected. A patient information leaflet will be given to you with your filled prescription and will provide many details concerning the use of ganirelix. Read the information carefully and ask your doctor for any additional information or explanation.

Sometimes ganirelix can be given by injection at home. If you are using this medicine at home:

  • Understand and use the proper method of safely preparing the medicine if you are going to prepare your own medicine.
  • Wash your hands with soap and water and use a clean work area to prepare your injection.
  • Make sure you clearly understand and carefully follow your doctor's instructions on how to give yourself an injection, including using the proper needle and syringe.
  • Do not inject more or less of the medicine than your doctor ordered.
  • Remember to move the site of injection to different areas to prevent skin problems from developing.
  • Throw away needles, syringes, bottles, and unused medicine after the injection in a safe manner.
  • Tell your doctor when you use your last dose of ganirelix. Your doctor will give you another medicine called human chorionic gonadotrophin (hCG) or arrange for you to get this medicine at the right time.


The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For injection dosage form:
    • For treatment of female infertility:
      • Adults—After receiving FSH treatment on Day 2 or 3 of your menstrual cycle, 250 micrograms (mcg) of ganirelix is injected under the skin once a day during the mid to late follicular phase (about Day 7 or 8 up to Day 12 or 13 of your menstrual cycle).
      • Children—Use is not recommended.

Missed Dose

Call your doctor or pharmacist for instructions.


Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.

Keep out of the reach of children.

Do not keep outdated medicine or medicine no longer needed.

Throw away used needles and syringes in a hard, closed container that the needles cannot poke through. Keep this container away from children and pets.

Ask your pharmacist, doctor, or nurse about the best way to dispose of any leftover medicine and other supplies.

Pregnancy & Lactation

Pregnancy Category: X

Lactation: Excretion unknown; not recommended

Pregnancy Categories

A:Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.

B:May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

C:Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.

D:Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.

X:Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.

NA:Information not available.


Mechanism of Action

Gonadotropin releasing-hormone antagonist; blocks endogenous LHRH in pituitary with high antagonistic activity & inhibits premature LH surges in patients undergoing controlled ovarian hyperstimulation; prevents ovulation until follicles are of adequate size


Half-Life: 12.8-16.2 hr (elimination)

Onset: Within 8 hr

Duration: <48 hr

Peak Plasma Time: ~1 hr

Bioavailability: 91%

Vd: 43.7 L (single dose); 76.5 L (multiple dosing)

Protein Bound: 82%

Metabolism: Liver

Total Body Clearance: 3-4 L/hr

Excretion: Feces (75%); urine (22%)


No information is available on the relationship of age to the effects of ganirelix injection in the pediatric population. Safety and efficacy have not been established.

Ganirelix Pregnancy Warnings

Ganirelix has been assigned to FDA pregnancy category X. Animal studies of ganirelix administered from day 7 to near term at dosages 0.4 to 3.2 times the human dosage (based on body surface area) failed to reveal an increase in fetal abnormalities. Fertility, physical, and behavioral characteristic of offspring were unchanged. The incidence of litter resorption was increased.