Efficacy on the risk of vertebral fracture with administration of once-weekly 17.5 mg risedronate in Japanese patients of established osteoporosis with prevalent vertebral fractures: a 156-week longitudinal observational study in daily practice

Currently, the only available evidence for the efficacy of once-weekly 17.5 mg risedronate in preventing vertebral fractures was obtained in a 48-week study in Japan. We performed a 156-week prospective, longitudinal, observational study to determine the efficacy of the 17.5 mg risedronate in preventing vertebral fractures. We included Japanese patients with established osteoporosis who were older than 50 years and had radiographically confirmed vertebral fractures. The primary endpoint was the incidence of vertebral fractures every 24 weeks, with the final interval spanning 36 weeks. We also calculated the change in bone mineral density of the lumbar spine (L2-4 BMD) and urinary N-telopeptide of type I collagen (u-NTX), and assessed the incidence of adverse drug reactions and the drug adherence rate. Data from 241 patients were available for analysis of vertebral fracture prevention. The incidence rate of vertebral fractures decreased in a time-dependent manner (P = 0.0006; Poisson regression analysis). The risk ratio (fracture incidence per 100 person-years in the final 36 weeks versus that in the first 24 weeks) was 0.21 (95 % confidence interval 0.08-0.55). Compared to baseline values, L2-4 BMD increased by 6.41 % at 156 weeks, while u-NTX decreased by 36 % at 24 weeks and was maintained thereafter (P < 0.0001). The incidence rate of adverse drug reactions was 9.18 %. Drug adherence rates assessed every 4 weeks were over 90 %. Our results indicate that 156 weeks of treatment with once-weekly 17.5 mg risedronate effectively reduced the risk of vertebral fracture in Japanese patients with established osteoporosis older than 50 years.