Abaloparatide Added to Ongoing Denosumab vs Continued Denosumab Alone

Some women on denosumab treatment for osteoporosis remain at high risk for fracture. These include women who sustain incident fractures on denosumab and those who have declining bone mineral density (BMD) or persistently low bone mineral density (BMD), despite treatment. There are few options available for these patients. Denosumab withdrawal is associated with dramatic increased bone remodeling, rapid prominent bone loss, and multiple vertebral fractures (Cummings JBMR 2017). Switching from denosumab to teriparatide is associated with substantial BMD loss in the hip and femoral neck. After 2 years of denosumab treatment, when women are switched to teriparatide, total hip BMD remains below the baseline (at end of denosumab treatment) over the entire 2 years of teriparatide treatment (Leder Lancet 2015). Abaloparatide might be a better option than teriparatide in patients switching from denosumab, because it is less pro-resorptive than teriparatide, however, hip BMD will still likely decline. Alternatively, adding abaloparatide to ongoing denosumab might be an excellent treatment option for these women. One of the investigators has previously shown that adding teriparatide to ongoing alendronate results in improved BMD and bone strength, compared to switching to teriparatide (Cosman JCEM 2009 and Cosman JBMR 2013). Others have shown that co-administration of teriparatide and denosumab to treatment naïve women increases BMD more than either agent alone (Tsai Lancet 2013, Leder et al JCEM 2014). Based on both of these observations, the investigators believe that adding abaloparatide to continued denosumab treatment will allow bone formation to increase, without increasing bone resorption (modeling-based bone formation) and will produce substantial BMD increments in both spine and hip. Hypothesis: In women who still appear to be at high risk for fracture while receiving ongoing denosumab therapy, adding abaloparatide will increase BMD of the lumbar spine and total hip significantly more than continuing denosumab alone.