Utilization and effectiveness of osteoporosis medications among medicare beneficiaries

Abstract

This dissertation contains three papers evaluating the utilization and effectiveness of osteoporosis medications using data on a 5% sample of Medicare beneficiaries in 2006-2009. The first paper assessed the completeness of Medicare Part D data on generic alendronate. The second paper sought to identify anti-osteoporosis medication utilization patterns and factors associated with medication discontinuation. The third paper examined the comparative effectiveness of osteoporosis medications for risk of fractures and mortality, with a focus on the recently introduced infusion and injection medications.

In the first study, we identified beneficiaries highly adherent with branded alendronate during 1/1/06-2/6/07 ("2007 cohort") and highly adherent during 1/1/07-2/6/08 ("2008 cohort"), and found the proportion presumably discontinuing bisphosphonate therapy was 9% in the 2008 cohort compared to 8% in the 2007 cohort (adjusted hazard ratio (HR), 1.15; 95% confidence interval (CI), 1.05-1.26). These results suggest that the missing claims for generic alendronate in 2008 Medicare data are not substantial, and misclassification of alendronate exposure after the introduction of generic products is minimal.

The second study identified individuals initiating bisphosphonate treatment and evaluated their medication status and switching pattern at the end of follow-up. Logistic regression analyses indicated that factors measured at the time of therapy initiation were at most weakly associated with discontinuation, regardless of the definition of discontinuation or length of follow-up. A case-crossover analysis using conditional logistic regression identified a number of factors that precipitate discontinuation after 12 months of high adherence, including more physician visits, hospitalization, bone density testing, higher Charlson score, higher drug payments, less medications, and upper gastrointestinal problems.

In the third study, to determine if fracture and mortality rates vary among patients initiating different anti-osteoporosis medications, we identified new users of intravenous (IV) zoledronic acid, oral bisphosphonates, IV ibandronate, calcitonin, raloxifene, or parathyroid hormone. Cox regression analyses using IV zoledronic acid as the referent group, indicated positive associations of IV ibandronate with hip fracture (adjusted hazard ratio (HR), 2.37; 95% CI, 1.25-4.51), calcitonin with vertebral fracture (HR=1.59, 95% CI, 1.04-2.43), and calcitonin with mortality (HR=1.31; 95% CI, 1.02-1.68).

In addition to specific findings, these studies collectively show that Medicare data provide valuable information on the utilization and effectiveness of medications for osteoporosis among older adults.