GnRH analogues in endometriosis

Summary points:

• used in treatment of endometriosis since early 1980s
  
  
• induce a reversible pseudomenopause
  
  
• bind to pituitary GnRH receptors and result in a stimulation of follicle-stimulating hormone (FSH) and luteinising hormone release; GnRH analogues have much longer half-life than natural GnRH and therefore the pituitary is exposed to continuous GnRH stimulation resulting in a down regulation of the pituitary and consequent reduction of FSH and LH levels. Oestrogen levels equivalent to postmenopausal levels are achieved within about 3 weeks of initiation of therapy
  
  
• side effects:
  • oestrogen deficiency related e.g. vaginal dryness, hot flushes, reduction of libido, bone loss
  • duration of GnRH analogue treatment is limited by side effects, especially bone loss (1); addback therapy is used to help prevent or reduce bone loss secondary to GnRH analogue therapy. Various addback therapies have been tried including progestogens, tibolone, bisphosphonates and combined oestrogen/progestogen. The addback therapy should not negate the treatment effect of the GnRH analogue on the endometriosis

Reference:

• 1) Johansen JS et al (1988). The effect of GnRH agonist on bone metabolism. J Clin Endocrinol Metab, 67, 701-6.