Bone Abstracts

Clinical trials suggest that denosumab (DEN) therapy results in greater increases in bone mineral density (BMD) in treatment-naive patients than in patients switched from bisphosphonates.

We retrospectively reviewed charts of all patients treated with DEN at an osteoporosis referral centre in Vancouver, Canada including all patients treated with DEN 60 mg SC every 6 months for 1 year or more, and in whom baseline and follow-up BMDs were available. BMD was followed at a single site, whichever of spine or hip was lower. Patients were either treatment-naive, or switched from alendronate, risedronate, zoledronic acid (ZOL), or teriparatide.

A total of 758 patients were included, 310 followed at hip and 448 followed at spine. All groups increased BMD on DEN. We defined a responder as being a patient with >3% increase in BMD at spine or total hip site at one year. In all groups, 65% of patients responded at spine and 34% responded at hip at one year. Responders increased to 87 and 52% at spine and hip respectively at 4 years. The greatest proportion of responders was in the treatment naïve group where at 1 year, 100% showed a response at spine and 83% showed a response at hip. Compared to other groups, patients switched from ZOL had fewer responders at hip and spine at 1 year and this difference persisted at 3 years at hip.

We observed a greater than expected BMD responder rate in patients switching from bisphosphonate to DEN as compared to published clinical trials. Lower adherence to prior therapy and the use of generic bisphosphonates in clinic patients may account for some of this difference. Our results will inform clinicians regarding the likelihood of seeing a significant BMD response when transitioning individual patients to DEN.