Adherence to bisphosphonates therapy and hip fracture risk in osteoporotic women

Abstract

Adherence is now one of the major issues in the management of osteoporosis and several papers have suggested that vertebral fractures might be increased in patients who do not follow appropriately their prescriptions. This paper relates the strong relationship existing between adherence to anti-osteoporosis treatment and the risk of subsequent hip fracture. A study was performed to investigate adherence to bisphosphonate (BP) therapy and the impact of adherence on the risk of hip fracture (Fx). An exhaustive search of the Belgian national social security database was conducted. Patients enrolled in the study were postmenopausal women, naive to BP, who received a first prescription of alendronate. Compliance at 12 months was quantified using the medication possession ratio (MPR). Persistence was calculated as the number of days from the initial prescription to a gap of more than 5 weeks after completion of the previous refill. A logistic regression model was used to estimate the impact of compliance on the risk of hip fracture. The impact of persistence on hip fracture risk was analysed using the Cox proportional hazards model. The mean MPR at 12 months was significantly higher among patients receiving weekly (n = 15.021) compared to daily alendronate (n = 14,136) (daily = 58.6%; weekly = 70.5%; p < 0.001). At 12 months, the rate of persistence was 39.45%. For each decrease of the MPR by 1%, the risk of hip Fx increased by 0.4% (OR: 0.996; CI 95%: 0.994-0.998; p < 0.001). The relative risk reduction for hip Fx was 60% (HR: 0.404; CI 95%: 0.357-0.457; p < 0.0001) for persistent compared to non-persistent patients. These results confirm that adherence to current therapeutic regimens remains suboptimal.