IntroductionDenosumab is an effective antiresorptive molecule and reduces the risk of fracture in postmenopausal osteoporosis. Cessation of denosumab therapy however is associated with rapid declines in bone mineral density (BMD), rises in bone remodeling, and an increased risk of fracture. We evaluated the effect of low dose denosumab (30 mg every 6 months) on the prevention of bone loss following a switch from standard dose (60 mg of denosumab every 6 months) in a prospective observational study.MethodsWe recruited 114 women 50–90 years of age with postmenopausal osteoporosis at a moderate fracture risk without prior fragility fractures, who had been on denosumab 60 mg every 6 month. These women switched to low dose denosumab 30 mg every 6 months. Mean percentage change in lumbar spine (LS), femoral neck (FN), total hip (TH) and 1/3 distal radius (1/3RAD) BMD at 12 and 24 months were evaluated. Predictors for change in BMD were explored. Subgroup analysis for patients on denosumab 60 mg every 6 months for <3 years and for ≥3 years before switching to low dose denosumab 30 mg was evaluated.ResultsAt 12 months following a switch from 60 mg to 30 mg of denosumab every 6 months we observed an increase in LS BMD mean percentage change (+2.03%, 95% CI 1.18–2.88,p< 0.001). BMD was stable at the hip and radial sites. Age was found to be a predictor of the mean percentage change in LS BMD for the overall sample. At 24 months, there was a further increase in LS BMD mean percentage change (+3.44%, 95% CI 1.74–5.12,p< 0.001), with stable BMD at other skeletal sites. The 12 month mean BMD percentage change at the LS (p= 0.015), FN (p< 0.001), TH (p< 0.001), and 1/3 RAD (p< 0.001) were found to be predictors of the 24 month mean BMD percentage change. No clinical fractures were reported during 24 months of follow up.ConclusionWe observed stable BMD following a switch from denosumab 60 mg every 6 months to 30 mg every 6 months in this prospective observational study conducted in postmenopausal women at a moderate fracture risk