Gonadotropin Releasing Hormone Analogues
Information about Gonadotropin Releasing Hormone Analogues
The gonadotropin releasing hormone (GnRH) agonists and antagonists are short peptide analogues of GnRH that cause a profound inhibition of estrogen and androgen synthesis and are used predominantly as androgen deprivation therapy of advanced prostate cancer. Some of these agents are also used to treat benign conditions responsive to hormonal inhibition such as endometriosis, uterine fibroids, precocious puberty and infertility. Leuprolide, goserelin, triptorelin and histrelin are considered GnRH agonists, whereas degarelix acts predominantly as an antagonist.
Liver safety of Gonadotropin Releasing Hormone Analogues
Several of the GnRH analogues have been reported to be associated with transient serum enzyme elevations during therapy, but none have been convincingly implicated in causing clinically significant liver injury with jaundice.
Mechanism of action of Gonadotropin Releasing Hormone Analogues
Gonadotropin releasing hormone is a decapeptide that is produced in the hypothalamus and acts upon GnRH receptors on the surface of gonadotropin cells in the pituitary gland, stimulating the release of luteinizing hormone (LH) and follicular stimulating hormone (FSH) which, in turn, stimulate the production and release of testosterone by the male testes and estrogen by the female ovaries and placenta. GnRH is typically produced in a pulsatile manner, and its synthesis is regulated by circulating levels of testosterone in men and estrogens in women. Infusions of GnRH agonists produce an initial transient increase in sex hormones, but with continued non-pulsatile stimulation, LH and FSH synthesis are inhibited and estrogen and testosterone levels decline. GnRH analogues have been found to be much more potent and sustained in action that the native decapeptide and have been used extensively in modulation of sex hormone synthesis. The GnRH analogue degarelix acts in a somewhat different manner in that it is an antagonist of the gonadotropin receptors in the pituitary and inhibit LH and FSH synthesis and release directly, and without an initial surge that is typical of the GnRH agonists. The ultimate effects and efficacy of the GnRH agonists and antagonist are similar, the difference being a more rapid onset and the lack of an initial surge in sex hormone release with the pure antagonist.
Brand name for Gonadotropin Releasing Hormone Analogues
The commercial names and year of approval in the United States of the currently available forms of GnRH agonists and antagonists are: leuprolide, also called leuprorelin (Lupron: 1985), goserelin (Zoladex: 1989), histrelin (Supprelin, Vantas: 1991 and 2004), triptorelin (Trelstar: 2000), and degarelix (Firmagon: 2008). Many of these agents are now available in generic forms as well. Long acting forms that allow for administration at 1, 3, 6 and even 12-month intervals are available for some GnRH analogues. The GnRH analogues all require parenteral (subcutaneous or intramuscular) administration and are used largely as androgen deprivation therapy for advanced prostate cancer. They are used off-label for precocious puberty, gender dysphoria and infertility.
Side effects of Gonadotropin Releasing Hormone Analogues
Common side effects of the GnRH agonists and antagonists include symptoms of hypogonadism such as hot flashes, gynecomastia, fatigue, weight gain, fluid retention, erectile dysfunction and decreased libido. Long term therapy can result in metabolic abnormalities, weight gain, worsening of diabetes and osteoporosis. Rare, but potentially serious adverse events include transient worsening of prostate cancer due to surge in testosterone with initial injection of GnRH agonists and pituitary apoplexy in patients with pituitary adenoma.
Drug class for Gonadotropin Releasing Hormone Analogues
Drug Class: antineoplastic agents, GnRH Analogues GnRH Analogues: Degarelix, Goserelin, Histrelin, Leuprolide, Triptorelin