To the Editor: In their observational study, Dr Ho and colleagues1 attributed a 9% increase in adverse outcomes to the attenuation of the benefit of clopidogrel through an interaction with PPIs. This exceeds by 400% the benefits of clopidogrel seen in the CURE trial2 and is consistent with the extreme unbalancing in measured covariates observed between the groups. Only measured covariates can be corrected at the analytical level, and it seems likely that residual confounding is present. Supporting this contention, the clopidogrel benefit in CURE was observed within 60 days, but the negative differences in the study by Ho et al were apparent only at a much later time. This is when residual confounders may have exerted their influence and is outside the benefit window currently attributed to clopidogrel after ACS.
Schneider-Lindner V, Filion KB, Brophy JM. Adverse Outcomes Associated With Use of Proton Pump Inhibitors and Clopidogrel. JAMA. 2009;302(1):29-31. doi:10.1001/jama.2009.897