Duration of Bisphosphonate Drug Holidays and Associated Fracture Risk

Background: Discontinuation of bisphosphonates (BP) or a "drug holiday" after several years of treatment is increasingly common. However, the association of drug holiday duration with future fracture risk is unclear. Objectives: We evaluated the rate of fracture in relation to various lengths of drug holidays among women receiving long-term BP therapy. Research Design: Observational cohort study using US Medicare data 2006-2016. Incidence rates (IRs) and Cox proportional hazards models were used to evaluate the rate and adjusted hazard ratios (aHRs) controlling for potential confounders. Subjects: Women aged 65 years and above enrolled in fee-for-service Medicare who had been adherent (>= 80%) to alendronate, risedronate, or zoledronate for >= 3 years. Measures: Hip, humerus, distal forearm, and clinical vertebral fracture. Results: Among 81,427 eligible women observed for a median (interquartile range) of 4.0 (2.5, 5.3) years, 28% of women underwent a drug holiday. In the alendronate cohort (73% overall), the IR of hip fracture among women who discontinued BP for >2 years was 13.2 per 1000 person-years. Risk was increased (aHR=1.3, 1.1-1.4) versus continuing therapy (IR=8.8, referent). Rates were elevated for humerus fracture with discontinuation >2 years (aHR=1.3, 1.1-1.66) and for clinical vertebral fracture with discontinuation >2 years (aHR=1.2, 1.1-1.4). Results were similar for risedronate, zoledronate, and ibandronate for hip and clinical vertebral fracture. Conclusion: Discontinuing alendronate beyond 2 years was associated with increased risk of hip, humerus, and clinical vertebral fractures.