Effect of Adherence on Lifetime Fractures in Osteoporotic Women Treated With Daily and Weekly Bisphosphonates

Patients miss doses of their osteoporosis medications, or stop taking them altogether, for a variety of reasons. Whereas the reasons have been well-studied, their consequences, at the population level, have not. The goal of this study was to estimate the number of fractures that could be prevented with optimal adherence compared with usual adherence to daily and weekly bisphosphonates in the United States (US). We developed a simulation of adherence to bisphosphonate therapy in the US. The model samples women by age and BMD from nationally representative US distributions, and tracks them over time assuming they are treated with a daily or weekly bisphosphonate. The model simulates two adherence scenarios: usual adherence and optimal adherence. The differences in fracture rates between these scenarios, as well as the medication and fracture costs, are estimated with the model. Approximately 258 (95% interval, 194-324) lifetime fractures can be prevented with optimal adherence per 1,000 bisphosphonate-treated women. For optimal adherence, these results translate to an additional lifetime medication cost of $3,800 and a lifetime savings in fracture-related costs of $2,100, for an expected net cost of $1,700 (95% interval, -$4,100 to $3,300) per woman over her lifetime. These results suggest that in patients taking daily or weekly bisphosphonate therapy, a substantial number of fractures occur that are attributable to less than optimal adherence. These results show that there is implicit value to improving adherence, both from a financial and clinical perspective. J Bone Miner Res 2009;24:1819-1826. Published online on May 4, 2009; doi: 10.1359/JBMR.090506