J Bone Miner Res. 2021 May 24.doi: 10.1002/jbmr.4333.
The role of mid-treatment monitoring dual-energy X-ray absorptiometry-bone mineral density (DXA-BMD) for bisphosphonate-treated patients with osteoporosis remains unsettled. A common reason for such monitoring is to encourage ongoing medication adherence. We sought to determine if a DXA-BMD treatment monitoring test was associated with improved medication adherence and whether improved adherence after a DXA-BMD treatment monitoring test was associated with subsequent reduction in fracture rates. Using linked administrative databases within Manitoba, Canada, we performed a retrospective cohort study of women starting and continuing antiresorptive therapy in whom a mid-treatment DXA-BMD monitoring test was performed. From the provincial pharmacy database, we estimated medication adherence by calculating annual medication possession ratio (MPR) and determining the change in MPR with respect to change (stable/decrease) in the DXA-BMD monitoring test, in addition to fracture rates before and after the test. The cohort comprised 3418 women, 90.7% treated with oral bisphosphonate, with pharmacy data for the 3 years before and after the mid-treatment DXA-BMD. Median (interquartile range) MPR was 0.84 (0.49-0.99) in the year before DXA-BMD and 0.84 (0.48-0.99) in the year after DXA-BMD (p = 0.37). Among those whose DXA-BMD declined, MPR in the prior year was 0.54 (0.04-0.92) but improved to 0.70 (0.31-0.92) in the year after DXA-BMD (p < 0.001). Among those whose DXA-BMD monitoring test was stable/improved, the fracture rate before the monitoring DXA-BMD was 10.1 per 1000 person-years and in those whose DXA-BMD monitoring test showed a decrease, the rate was 23.7 per 1000 person-years (p < 0.001). Despite improved adherence in those with DXA-BMD decline, the post DXA-BMD fracture rate was 22.4 per 1000 person-years versus 12.9 per 1000 person-years in those who had stable DXA-BMD (p < 0.001). A mid-treatment DXA-BMD reassessment strategy may be useful to focus attention upon adherence, but for optimal fracture outcomes, treatment adherence should be specifically addressed at the commencement of therapy.