Cetrotide and Ganirelix (Antagon) in IVF

Cetrotide and Ganirelix(GnRH Antagonists)

Cetrotide (cetrorelix) and ganirelix (Antagon) are examples of a type of medication that is used to prevent premature ovulation. This class of medications is referred to as GnRH antagonists or simply antagonists. Cetrotide and Antagon are newer medications than Lupron but have become tremendously popular as a result of their easy of use and high pregnancy rates.

Medications which work rapidly

Cetrotide and Ganirelix exert their action on the pituitary gland. The pituitary is responsible for producing the hormones which stimulate egg growth and development and for triggering ovulation of a mature egg. During an in vitro fertilization cycle, the physician needs to prevent ovulation from occurring so the eggs can be removed directly from the ovary.

In the early days of IVF, before medications to prevent ovulation were available, about 25% of IVF cycles would be cancelled for premature ovulation. Then a medication called Lupron was used to block the pituitary from causing premature ovulation. Lupron caused a few problems, however. When Lupron is first administered to a woman, it would stimulate her pituitary gland for several days before it would eventually suppress it. This is known as the stimulation or flare phase. The flare phase required that women start Lupron a few weeks before she could begin the fertility medications required for stimulation of the ovary. In some women, the flare effect can cause the development of cysts in the ovaries that could further delay the start of fertility medications.

A primary advantage of Cetrotide and Ganirelix is that they do not have a “flare phase”. Down regulation (suppression) of the pituitary occurs immediately. Therefore, it is not necessary to start these medications before the fertility medications begin (see picture). Cetrotide or Ganrelix would normally be started after 4-6 days after the start of the fertility medications. This shortens the number of days that a woman must take injections.

Protocol for using Cetrotide and Ganirelix

Fertility medications such as Follistim or Gonal F are the first injections which are administered in an antagonist cycle. The fertility medications may be started on the second or third day after the onset of a period or after a woman has been on birth control pills (oral contraceptives). A baseline assessment of hormones by blood test and the ovaries by ultrasound are performed at some point before the fertility medications are started.

Ganirelix Acetate Injection is available in disposable, pre-filled, ready to inject syringes containing 250 micrograms of ganirelix acetate. Mixing is not required. Ganarelix is designed to be self-injected using the supplied syringe for injection just under the skin (subcutaneous).

There are two protocols for beginning the Cetrotide or Ganirelix. One method, called the flexible start, utilizes the results of the blood and ultrasound monitoring of egg development. Once development of the eggs has started to occur, the Cetrotide or Ganirelix is started. A second method, called the fixed start, will begin the Cetrotide and Ganirelix after a certain number of days of fertility medication have been given regardless of the results of blood and ultrasound monitoring.

The GnRH antagonists are continued along with the fertility medication until the last day of fertility medication is given. Typically this means a woman will have 4-6 days of Cetrotide or Ganirelix before the egg retrieval.

Some experts believe that IVF cycles that use Lupron for pituitary suppression, may cause some women to become “over-suppressed” and therefore not respond as well to the fertility medications. Whether this occurs or not is subject to some debate. However, with the use of antagonists, there is no concern for this problem.

Learn about Preparing and using Cetrotide for IVF.
Learn about Preparing and using Ganirelix for IVF.
Learn about Fertility drugs to stimulate eggs for IVF.
Learn about administering a subcutaneous injection