Efficacy of Low Dose Denosumab in Maintaining Bone Mineral Density in Postmenopausal Women With Osteoporosis Switching From 60mg to 30mg 6 Monthly: A Real World, Prospective Observational Study

Introduction: Denosumab, a fully human monoclonal antibody to RANK-ligand, has been shown to increase bone mineral density (BMD) and reduce the risk of fracture in postmenopausal women with osteoporosis. Cessation of denosumab is associated with rises in bone remodelling, reductions in BMD and an increased risk of fracture. The primary objective of this study is to evaluate the efficacy of low dose denosumab (30mg/6 months) in preventing bone loss in postmenopausal women with osteoporosis switching from 60mg to 30mg every 6 months. We report the effects of low dose denosumab for upto 2years in patients previously treated with denosumab for >=3 years as well as < 3years. Methods: Following informed consent, postmenopausal women with osteoporosis who had been on denosumab 60mg every 6 months were switched to receive 30mg of denosumab every 6 months.. Patients with an additional skeletal disorder, prior fragility fracture, or on oral steroids (daily in the past 12 months) were excluded. The primary endpoint was the percent change in BMD at the lumbar spine (LS), total hip (HP), femoral neck (FN) and 1/3 radius (1/3R) at 12 and 24 months. Secondary outcomes were adverse effects and fracture Results: 127 patients were included in the study. 44 patients had received 60 mg for 3 years or longer before transitioning to 30mg and 83 patients switched before completing 3 years on full dose therapy. Patients on less than 3yrs of 60mg therapy before the switch showed a significant improvement in BMD at LS (+2.00%, 95% CI 0.49% to 3.51%, n = 55, p-value = 0.01) 1 year post transition. There were no significant changes at the FN, TH or 1/3 radial sites 1 year post transition compared to baseline. At 2 years post transition (n=35) significant changes were noticed at LS (+4.65%, 95% CI 2.29% to 7.01%, p value <0.001), FN (+ 4.87%, 95% CI 1.46% to 8.28%, p value = 0.006) and 1/3 radial sites (+4.95%, 95% CI 0.73% to 9.17%, p value = 0.02). No significant changes were noted at TH. Similar results were seen with prior denosumab therapy for <3years No fractures were observed in this observational study. Conclusions: Switching from 60mg of denosumab to 30 mg every 6 months was not associated with reductions in BMD and may be a valuable treatment option in patients who have completed long term denosumab therapy.