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Fertility Drugs- Lupron (GnRH Agonist), Ganirelix,
Cetrotide (GnRH antagonist)
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GnRH is produced by the hypothalamus and travels through the bloodstream to the pituitary where it controls the production of FSH and LH. The hypothalamus works like a “thermostat” and increases, or decreases, the production of GnRH based upon hormone levels. For example, as estrogen levels increase signaling follicular development, the hypothalamus begins to reduce FSH production.
Lupron, a commonly used fertility drug, works by competing with receptors at the hypothalamus while Cetrotide and Ganirelix work to directly block GnRH at the pituitary. Since Ganirelix and Cetrotide block GnRH, they produce a more profound, and quicker, down regulation. Patients undergoing ovulation induction with the fertility drug FSH must come to our office regularly for estradiol hormone measurements and ultrasound evaluation.
In order for ovulation to occur, the hypothalamus must signal the pituitary gland to release a surge of LH. This cannot occur while a patient is taking Lupron, Ganirelix or Cetrotide because the action of GnRH on the pituitary is blocked. This is the primary reason these drugs are used in assisted reproductive technology (ART) cycles. Ovulation must not occur prior to egg retrieval or the stimulation cycle would be “lost”. When the eggs are mature an injection of hCG (the body reacts to hCG like LH) is given and retrieval is scheduled.
One characteristic of Lupron therapy is that there is an initial spike in FSH production when the drug is first started followed by dramatic suppression. The “flare protocol” makes use of this physiologic characteristic by beginning FSH during the initial suppression resulting in higher initial FSH levels.
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