Background:
Substitution from brand-name to generic drugs is one way to reduce costs of pharmacological treatments. Generic drugs licensing is obtained through comparative bioavailability studies for which a variation of up to 20% is generally accepted. However, “real-life” efficacy and tolerance of generic drugs are not studied prior to commercialization. We aimed to evaluate the impact of brand-name to generic losartan, valsartan or candesartan substitution on serious adverse events (hospitalizations, emergency room consultations [ER] or mortality).
Method:
Three cohorts of persistent angiotensin II receptor blockers (ARB) users (losartan [brand-name and 8 generics], valsartan [brand-name and 5 generics] and candesartan [brand-name and 3 generics])aged ≥ 66 years were constituted using data from the Quebec Integrated Chronic Disease Surveillance System. Generic exposition was determined by substitution time-distribution matching. Time free of adverse events up to 365 days after the onset of generic exposition was compared between groups by survival analysis using Cox regression models adjusted for age, sex, comorbidities, concomitant treatments, socioeconomic status, previous brand-name drug, healthcare resources utilization and prescriber’s speciality, to provide hazard ratio (HR). Sensitivity analysis including non-persistent users was also conducted.
Results:
Within cohorts (losartan, n = 15,469; valsartan, n = 17,205; and candesartan, n = 25,008), proportions of exposed to generic substitution vs. unexposed who had at least one adverse event were respectively: 35% vs. 25%, 34% vs. 28% and 31% vs. 27% (all,
p
<0.0001). When adjusted for potential confounders, risk of hospitalizations and ER were higher for those exposed to generic substitution. Specifically, HR for exposed to generic substitution are the following for losartan, valsartan and candesartan: hospitalizations (HR: 1.23 [
p
< 0.0001]; 1.22 [
p
< 0.0001] and 1.08 [
p
= 0.0317]) and ER (HR: 1.55; 1.20 and 1.16, all =
p
< 0.0001). Regarding mortality, HR were respectively: 0.63 [
p
= 0.1456]; 0.95 [
p
= 0.8487] and 0.43 [
p
< 0.0001]). Survival was not significantly different for exposed to generic losartan and valsartan substitution. However, even if the time free of hospitalizations and ER was 8% and 16% shorter for patients exposed to generic candesartan substitution, their survival was 2.3 times better when compared to patients who remained on brand-name candesartan (unexposed). Sensitivity analysis yield similar results.
Conclusion:
Substitution to generic antihypertensive drugs is associated with a significantly reduced delay before hospitalizations and ER for the three ARBs but a better survival for patients exposed to generic candesartan substitution only. Better bioavailability of generics versions of candesartan or differences in health cares between users could explain these differences.
CHALLENGES FOR GENERIC DRUG PRODUCERS
