Association of teriparatide adherence and persistence with clinical and economic outcomes in Medicare Part D recipients: a retrospective cohort study

BACKGROUND Improper medication adherence is associated with increased morbidity, healthcare costs, and fracture risk among patients with osteoporosis. The objective of this study was to evaluate the healthcare utilization patterns of Medicare Part D beneficiaries newly initiating teriparatide, and to assess the association of medication adherence and persistence with bone fracture. METHODS This retrospective cohort study assessed medical and pharmacy claims of 761 Medicare members initiating teriparatide in 2008 and 2009. Baseline characteristics, healthcare use, and healthcare costs 12 and 24 months after teriparatide initiation, were summarized. Adherence, measured by Proportion of Days Covered (PDC), was categorized as high (PDC ≥ 80%), moderate (50% ≥ PDC < 80%), and low (PDC < 50%). Non-persistence was measured as refill gaps in subsequent claims longer than 60 days plus the days of supply from the previous claim. Multivariate logistic regression evaluated the association of adherence and persistence with fracture rates at 12 months. RESULTS Within 12 months of teriparatide initiation, 21% of the cohort was highly-adherent. Low-adherent or non-persistent patients visited the ER more frequently than did their highly-adherent or persistent counterparts (χ2 = 5.01, p < 0.05 and χ2 = 5.84, p < 0.05), and had significantly lower mean pharmacy costs ($4,361 versus $13,472 and $4,757 versus $13,187, p < 0.0001). Furthermore, non-persistent patients had significantly lower total healthcare costs. The healthcare costs of highly-adherent patients were largely pharmacy-related. Similar patterns were observed in the 222 patients who had fractures at 12 months, among whom 89% of fracture-related costs were pharmacy-related. The regression models demonstrated no significant association of adherence or persistence with 12-month fractures. Six months before initiating teriparatide, 50.7% of the cohort had experienced at least 1 fracture episode. At 12 months, these patients were nearly 3 times more likely to have a fracture (OR = 2.9, 95% C.I. 2.1-4.1 p < 0.0001). CONCLUSIONS Adherence to teriparatide therapy was suboptimal. Increased pharmacy costs seemed to drive greater costs among highly-adherent patients, whereas lower adherence correlated to greater ER utilization but not to greater costs. Having a fracture in the 6 months before teriparatide initiation increased fracture risk at follow-up.