Alendronate medication possession ratio and the risk of second hip fracture: an 11-year population-based cohort study in Taiwan.

Abstract

Alendronate is effective in preventing second hip fracture in osteoporotic patients. However, no consensus exists on the accurate medication possession ratio (MPR) that is effective in preventing a second hip fracture. Our objective was to compare the risk of second hip fracture in patients treated with different MPR of alendronate. In this population-based cohort study, data from National Health Insurance Research Database of Taiwan were analyzed. Patients 50years and older who had an index hip fracture and were not receiving any osteoporotic medications before their fracture during 2000-2010 were included. The cohort consisted of 88,320 patients who were new alendronate users (n = 9278) and non-users (n = 79,042). Those without alendronate were matched 4:1 as the control group. Patients were subdivided into those with no medication, MPR < 25%, MPR 25-50%, MPR 50-75%, and MPR 75-100%. Cox proportional hazard models were used to calculate the adjusted hazard ratios for different MPRs of alendronate. After matching, 38,675 patients were included in this study; 20,363 (52.7%) were women, and 30,940 (80%) patients were without medication of alendronate. During follow-up on December 31, 2012, 2392 patients had a second hip fracture, for an incidence of 1449/100,000 person-years. Patients with alendronate MPR 50-75% had a lower risk of a second hip fracture compared to non-users (hazard ratio 0.66). When the MPR increased to 75-100%, the hazard ratio decreased to 0.61. In this population-based cohort study, risk of a second hip fracture can be reduced when the alendronate MPR is ≥ 50% for the year following the index hip fracture. As the MPR increases, the risk of a second hip fracture decreases.