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Pharmacotherapeutic Group: LHRH-Antagonist. ATC Code: G03X.
Pharmacology: Cetrotide inhibits the effects of a natural hormone, called luteinising hormone (LHRH). LHRH regulates the secretion of another hormone, called luteinising hormone (LH), which induces ovulation during the menstrual cycle. Cetrotide inhibits premature ovulation which is undesirable during hormone treatment for ovarian stimulation as only mature egg cells are suitable for fertilization.
Pharmacodynamics: Cetrorelix is a luteinising hormone releasing hormone (LHRH) antagonist. LHRH binds to membrane receptors on pituitary cells.
Cetrorelix competes with the binding of endogenous LHRH to these receptors. Due to this mode of action, cetrorelix controls the section of gonadtropins (LH and FSH).
Cetrorelix dose-dependently inhibits the secretion of LH and FSH from the pituitary gland. The onset of supression is virtually immediate and is maintained by continuous treatment, without initial stimulatory effect.
In females, cetrorelix delays the LH surge and consequently ovulation. In women undergoing ovarian stimulation the duration of action of cetrorelix is dose dependent. Following a single dose of cetrorelix 3 mg a duration of action of at least 4 days has been evaluated.
On day 4 the supression was approximately 70%. At a dose of 0.25 mg per injection repeated injections every 24 hrs will maintain the effect of cetrorelix.
In animals as well as humans, the antagonistic hormonal effects of cetrorelix were fully reversible after termination of treatment.
Pharmacokinetics: The absolute bioavialability of cetrorelix after SC administration is about 85%.
The total plasma clearance and the renal clearance are 1.2 mL x min-1 kg-1 and 0.1 mL x min-1 x kg-1, respectively. The volume of distribution (Vd/area) is 1.1 l x kg-1. The mean terminal half-lives following IV and SC administration are about 12 hrs and 30 hrs, respectively, demonstrating the effect of absorption processes at the injection site. The SC administration of a single dose (cetrorelix 0.25-3 mg) and also daily dosing over 14 days show linear kinetics.
