Timing of anti-osteoporosis medications initiation after a hip fracture affects the risk of subsequent fracture: A nationwide cohort study.

Objective: The optimal time after hip fracture to start prophylactic anti-osteoporosis medications (AOMs) remains uncertain, especially in real-world practice. Therefore, we investigated how timing of AOMs initiation affects the risk of subsequent osteoporotic fractures, and what factors influence timing of AOMs prescription.

Method: Patients ≥50 years old with diagnostic codes indicating hospitalization for hip fracture (n = 77,930) were identified from the Taiwan National Health Insurance Research Database; 9986 who were prescribed AOMs ≤1 year after a newly-diagnosed hip fracture were grouped into those who started AOMs from: ≤14 days (very early); 15-84 days (early); 85-252 days (late); and 253-365 days (very late). Associations with fracture-related hospitalizations after an index fracture were analyzed using a multivariate, time-dependent Cox proportional hazards model, and between-group differences compared by log-rank testing. Factors influencing timing of AOMs initiation were elucidated using multivariate logistic regression analyses.

Results: Compared to AOMs initiation from 15 to 84 days, initiation after 252 days was associated with significantly increased risk of fracture-related hospitalization (HR = 1.93, 95% CI 1.29-2.89). Both sensitivity and pre-specified subgroup analyses yield similar results. Among patients with high adherence to AOMs, the increased risk of subsequent fracture-related hospitalization among very late users was profound (HR = 2.56, 95% CI 1.41-4.64).

Conclusion: Timing of AOMs initiation was significantly associated with age, index year, index hospital length of stay as well as the accreditation level and geographic region of index hospital. After adjusting factors associated with timing of AOMs initiation and patients' adherence, the anti-fracture benefit of AOMs still depends crucially on the timely initiation of AOMs.