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Once the patent of a brand-name drug expires, generic drugs are commercialized, and substitution from brand-name to generics may occur. Generic drug equivalence is evaluated through comparative bioavailability studies. Few studies have assessed outcomes after generic drug commercialization at a population level. We evaluated the impact of 3 generic angiotensin II receptor blockers commercialization on adverse events: hospitalizations or emergency room consultations.This is an interrupted time series analysis using the Quebec Integrated Chronic Disease Surveillance System. Rates of adverse events for losartan, valsartan, and candesartan users (N=136 177) aged ≥66 years were calculated monthly, 24 months before and 12 months after generics commercialization. Periods before and after generics commercialization were compared by negative binomial segmented regression models. Sensitivity analyses were also conducted. For all users, there was a monthly mean rate of 100 adverse events for 1000 angiotensin II receptor blocker users before and after generic commercialization. Among generic users of losartan, valsartan, and candesartan, there was an increase in rates of adverse events of 8.0% (difference of proportions versus brand-name, 7.5% [95% confidence interval, −0.9% to 15.9%]; P=0.0643), 11.7% (difference of proportions, 17.1% [95% confidence interval, 9.9%–24.3%]; P<0.0001), and 14.0% (difference of proportions, 16.6% [95% confidence interval, 7.9%–25.3%]; P<0.0001), respectively, the month of generic commercialization. The monthly trend of adverse events was affected for generic versus brand-name losartan users only (difference of proportions, 2.0% [0.7%–3.4%]; P=0.0033) ≤1 year after generics commercialization. Similar results were found in sensitivity analyses.Among generic users, immediate or delayed differences in adverse events rates were observed right after generic commercialization for 3 antihypertensive drugs. Rates of adverse events remained higher for generic users. Increases were more pronounced for generic candesartan, which is the studied product with the largest difference in comparative bioavailability. Risk and survival analysis studies controlling for several potential confounding factors are required to better characterize generic substitution.