Add-back therapy in the treatment of endometriosis: the European experience

Add-back hormone replacement therapy (HRT) can alleviate the undesirable hypo-oestrogenic effects of the gonadotrophin-releasing hormone (GnRH) agonists, including loss in bone mineral content. However, this approach presents a dilemma in patients with endometriosis as the re-introduction of oestrogen could re-stimulate the endometriotic process. There have been three recently published European studies investigating the combination of GnRH agonist plus add-back HRT in the treatment of endometriosis. The loss of bone mineral density was significantly diminished in a study using 25 micrograms oestradiol patches combined with continuous medroxyprogesterone acetate (5 mg). Neither this low oestrogen dose nor a full bone-sparing dose of oral oestradiol (2 mg daily) reduced the efficacy of Zoladex (goserelin acetate) in patients with endometriosis. Furthermore, in a small open study the gonadomimetic tibolone totally prevented the loss of bone structure during GnRH agonist therapy. If a GnRH agonist is considered the treatment of choice, then HRT should be used in combination.