Estimating the Effect of Elagolix Treatment for Endometriosis on Postmenopausal Bone Outcomes: A Model Bridging Phase III Trials to an Older Real-World Population

Elagolix, a gonadotrophin-releasing hormone antagonist, is used in premenopausal women with endometriosis. There is a risk of bone loss with elagolix, but the long-term effects of BMD loss later in life cannot be directly assessed and has not been quantified. To address this gap in knowledge, this study indirectly estimated the impact of elagolix on postmenopausal fracture risk. BMD change in premenopausal women with endometriosis treated with elagolix was modeled from the phase III program data (elagolix group) and used to simulate treatment effects on (fracture risk assessment tool estimated) 10-year risks of hip and major osteoporotic fracture in women ages 50 to 79 years from the 2005-2010 National Health and Nutrition Examination Survey (NHANES; ;N = 2303). Change in the proportion of women reaching risk-based antiosteoporotic treatment thresholds was also estimated. For elagolix versus NHANES, median 10-year risk of major osteoporotic fracture was 4.73% versus 4.70% in women ages 50 to 59 years, 7.03% versus 6.97% in women ages 60 to 69 years, and 10.83% versus 10.68% in women ages 70 to 79 years. Median 10-year risk of hip fracture in these same groups was 0.19% versus 0.18% for women ages 50 to 59 years, 0.51% versus 0.49% for women 60 to 69 years, and 2.22% versus 2.14% for women 70 to 79 years. The proportion of women reaching risk-based antiosteoporotic treatment thresholds caused by elagolix 150 mg daily for 12 months was 0.36% higher at age 50 to 59 years, 0.23% at age 60 to 69 years, and 1.79% at age 70 to 79 years. The number needed to harm was 643 for one additional hip fracture and 454 for one additional major osteoporotic fracture. Results were similar for elagolix 200 mg twice a day for 3 months. In the modeled scenarios, elagolix had minimal impact on long-term risk of fracture and reaching risk-based treatment thresholds.