Effect of denosumab on bone mineral density in patients with prior bisphosphonate exposure

Abstract

Objectives: It has been demonstrate that denosumab can effectively improve the BMD of patients with short-term (6 months) exposure of oral bisphosphonate. The aim of this study is to evaluate the change in BMD after switching to denosumab for one year in patients with prior oral bisphosphonate use for a longer duration. Material and Methods: Patients with osteoporosis were followed according to a standard protocol. Patients using denosumab for more than one year, with history of bisphosphonate exposure for at least one year, were recruited for analysis. Patients were monitored regularly in nurse-led clinic to ensure good drug adherence. Subcutaneous denosumab injection was administered by nurses as outpatient. BMD was measured by DXA scan. All subjects had adequate calcium and vitamin D supplementation. The BMD of the total spine, neck of femur and total hip before and after commencement of denosumab was compared by dependent T-test. Results: 104 female subjects with a mean age of 73.7 ± 10.5 years were included in this report. All of the subjects had history of fragility fracture. Duration of oral bisphosphonate exposure before switching to denosumab was 4.5 ± 2.7 years. The oral bisphosphonate used was alendronate 70 mg once weekly. There was no statistically significant difference observed in BMD of the total spine (0.655 ± 0.105 vs. 0.662 ± 0.107 g/cm2 , p= 0.24), neck of femur (0.485 ± 0.080 vs. 0.480 ± 0.080 g/cm2 , P= 0.30) and total hip (0.589 ± 0.109 vs. 0.598 ± 0.112 g/cm2 , p= 0.09) before and 1 year after initiation of denosumab. Conclusions: Patients with prevalent fragility fracture, despite having relatively long history of bisphosphonate exposure, should be benefited by continuation of anti-osteoporosis treatment because of high fracture risk. However, switching this group of patients to denosumab may not reproduce the similar BMD improvement observed in patients who had taken bisphosphonate for short term. However, the efficacy of denosumab in fracture risk reduction in this group of patients needs further evaluation.