Review on antagonists

Abstract

Gonadotropin-releasing hormone (GnRH) antagonists have been a breakthrough in reproductive medicine. The third generation antagonists (cetrorelix and ganirelix) do not have histamine releasing capability in the used doses. The competitive blockade of GnRH receptors by GnRH antagonists leads to an immediate but reversible arrest of gonadotropin secretion. Antagonists can be used as single-dose or multiple dose protocol in a fixed or flexible approach during ovarian stimulation to prevent premature luteinizing hormone surge. The stimulation remains close to the normal cycle, and more convenient and friendly to the patient with lesser dose and duration of stimulation. Recent Cochrane analysis suggests that there is no significant difference in the live birth rate when antagonists are compared with agonists (OR 0.86) and there is a significant reduction in the incidence of ovarian hyperstimulation syndrome (OHSS) (OR 0.43) with the use of antagonists. Gonadotropin-releasing hormone antagonists are of special benefit for use in patients with polycystic ovaries where agonist trigger can be used and OHSS can be prevented completely. Gonadotropin-releasing hormone antagonists have particular advantage in poor responders with lesser pituitary suppression in the early part of cycle. Gonadotropinreleasing hormone antagonists can be used in modified natural cycle, intrauterine insemination cycles, and frozen embryo transfer cycles. Novel uses of antagonists include suppression of established OHSS, and in various gynecological conditions (endometriosis, fibroids, precocious puberty).