Divergent Patterns of Antifracture Medication Use Following Fracture on Therapy: A Population-Based Cohort Study

Abstract

Context: Fracture on therapy should motivate better antifracture medication adherence. Objective: This study aimed to describe osteoporosis medication adherence in women before and following a fracture. Methods: This retrospective cohort analysis of antifracture medication possession ratios (MPR) among women in the Manitoba BMD Registry (1996-2013) included menopausal women who started antifracture drug therapy after a dual-energy X-ray absorptiometry (DXA)-BMD assessment with follow-up for 5 years during which a nontraumatic fracture occurred at least 1 year after starting treatment. Linked prescription records determined medication adherence (estimated by MPR) in 1-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); when 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 reemphasize treatment adherence.