Background: Federal standards authorize the commercialization of generic medicines after bioequivalence versus the brand-name originator has been demonstrated. For drugs with narrow therapeutic indexes, such as warfarin, the accepted difference in bioavailability is ≤ 10%. No systematic pharmacovigilance studies are conducted once generics become available.
Objective: We aimed to assess the impact of the arrival of generic warfarin on hospital visit trends (hospital admissions or emergency room consultations) in warfarin users.
Methods: This was an observational interrupted time series analysis (2 January 1996 to 1 January 2016). Using the Québec Integrated Chronic Disease Surveillance System, we included all patients who were aged ≥ 66 years, publicly covered and using brand-name or generic warfarin (N = 280,158). We estimated rates of hospital visits in 6-month periods, 5 years before and up to 15 years after the arrival of generic warfarin. Periods before and after were compared using segmented regression models for all users along with exploratory (generic vs. brand name)/subgroup analyses (cardiovascular comorbidities and socioeconomic status).
Results: Generic warfarin arrived on the market on 2 January 2001. Over the 20-year period of the study, the mean rate of hospital visits was 113 for 100 brand-name or generic users per 6-month period and was similar before and after the arrival of the generics. Up to 15 years after the arrival of the generics, the rates of hospital visits were 10% higher for generic than for brand-name users, which was confirmed by subgroup analyses.
Conclusions: Overall, we observed no impact on hospital visits after the arrival of generic warfarin in all the population treated with any type of warfarin. However, a higher crude rate of hospital visits among generic users than brand-name users remains to be validated using a different methodology and specific outcomes.