Zoladex (goserelin acetate), marketed by AstraZeneca, is approved by the U.S. Food and Drug Administration (FDA) for the treatment of endometriosis, and as a palliative treatment for prostate and breast cancer.
Zoladex is an implant injected every month under the skin. The implant gradually dissolves and releases the medication over time.
How Zoladex works
Estrogen is one of the key hormones working to thicken endometrial tissue that lines the uterus during the menstrual cycle, which later breaks down and leaves the body through menstrual bleeding.
GnRH is a hormone that regulates the levels of estrogen and other reproductive hormones. It is produced in the brain and binds to receptors in the pituitary gland. This binding stimulates the production of two hormones, follicle stimulating hormone (FSH) and luteinizing hormone (LH), which leads to an increase in estrogen levels.
Zoladex is a GnRH-agonist, or man-made compound that acts in similar ways to the natural compound. It binds to the same receptors as GnRH itself and plays a similar role, initially increasing the production of FSH and LH. But GnRH agonists bind very strongly to GnRH receptors and dissociate from them very slowly. In response to this continuous stimulus, the pituitary gland shuts down GnRH receptors and consequently becomes insensitive to the action of GnRH agonists. GnRH-agonists thereby suppress estrogen synthesis by the ovaries, which stops the menstrual cycle.
In endometriosis, estrogen also stimulates the growth of endometriotic lesions outside the uterus. By reducing estrogen levels, Zoladex inhibits the growth of these lesions and endometriosis-associated symptoms.
Zoladex in clinical trials
A multicenter, randomized trial compared the efficacy and safety of Zoladex and danazol. A total of 307 patients with endometriosis were randomized to receive either a monthly 3.6 mg depot of Zoladex via subcutaneous injection, or 200 mg oral danazol three times a day. Withdrawal rates were 6.4 percent of patients in the Zoladex group and 20.4 percent in the danazol group.
Endometriotic lesions significantly decreased in both treatment groups, with no notable differences between the groups. According to researchers, pelvic symptoms of endometriosis (both pain and lesions) were reduced in all patients after 24 weeks of treatment compared to baseline (study start). Among patients who were infertile at baseline, 29.3 percent in the Zoladex group conceived within 12 months after cessation of treatment, as did 24.1 percent of those in the danazol group.
A randomized Phase 4 clinical trial (NCT01682642) evaluated if Zoladex use might improve the success of in vitro fertilization (IVF) after surgery to remove lesions. Endometriotic lesions were removed by laser vaporization in the study’s 120 participants. The patients were then randomized to be treated with Zoladex or to receive no further treatment for three months before starting IVF treatment.
No difference was seen in the number of oocytes (eggs) that were retrieved for IVF. In both groups, about 39 percent of women became pregnant.
A randomized clinical trial (NCT02779387) at the University of People’s hospital in Peking, China, is planned to assess how Zoladex treatment might affect pregnancy rate. The study is reported to have opened in 2016, but is not yet marked as recruiting.
Another randomized clinical trial (NCT0371787), planned to start in October 2019, will evaluate the effect of treatment with GnRH-agonists — Zoladex, Dicapeptyl (triptorelin) and Lupron (leuprolide) — on IVF after surgical removal of endometrial lesions. The study will take place in Italy, and is not yet recruiting endometriosis patients with infertility.
Common side effects of Zoladex use include hot flushes, acne, oily hair and skin, and a reduction in libido. Rarely, women enter natural menopause while being treated with Zoladex and will not resume having periods after cessation of the treatment.
Zoladex should not be used for longer than six months because low estrogen levels can lead to a loss of calcium in the bones, making them fragile.
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