Divergent patterns of anti-fracture medication use following fracture on therapy: A population-based cohort study
Abstract Context Fracture-on-therapy should motivate better anti-fracture medication adherence. Objective Describe osteoporosis medication adherence in women before and following a fracture. Design Retrospective cohort study. Setting Manitoba BMD Registry (1996-2013). Patients Women who started anti-fracture drug therapy after a DXA-BMD with follow-up for 5 years during which a non-traumatic fracture occurred at least one year after starting treatment. Main Outcome Linked prescription records determined medication adherence (estimated by medication possession ratios, MPR) in one-year intervals. The variable of interest was MPR in the year before and after the year in which the fracture occurred with subgroup analyses according to duration of treatment pre-fracture. We chose an MPR of ≥0.50 to indicate minimum adherence needed for drug efficacy. Results There were 585 women with fracture-on-therapy, 193(33%) had hip or vertebral fracture. Bisphosphonates accounted for 82.2% of therapies. Median MPR the year prior to fracture was 0.89(IQR 0.49-1.0) and 0.69(IQR 0.07-0.96) the year following the year of fracture(p< 0.0001). The percentage of women with MPR ≥ 0.5 pre-fracture was 73.8%, dropping to 57.3% post-fracture(p<0.0001); restricted to hip/vertebral fracture results were similar (58.2% to 33.3%, p <0.002). Among those with pre-fracture MPR <0.5, only 21.7% achieved a post-fracture MPR ≥ 0.5. Conclusions Although fracture-on-therapy may motivate sustained/improved adherence, MPR remains low or even declines after fracture in many. This could reflect natural decline in MPR with time but is paradoxical to expectations. Fracture-on-therapy represents an important opportunity for clinicians to re-emphasize treatment adherence.