Not all aspirin products have equivalent antiplatelet efficacy-Aspirin formulated with magnesium stearate is less effective in preventing ischemic stroke.

PURPOSE Magnesium stearate (MgSt) is a widely used excipient in pharmaceutical formulations but should be avoided in aspirin preparations as it hydrolyzes aspirin. We hypothesized that preparations of aspirin-containing MgSt (MgSt-ASA) are less effective in preventing thrombosis in clinical settings. The risk of composite cardiovascular events in patients treated with MgSt-ASA preparations for preventing secondary stroke was evaluated. METHODS This retrospective cohort study used Taiwan's claims data from 1997 to 2013. Patients who were discharged after ischemic stroke (IS) and administered with only MgSt-ASA or non-MgSt-ASA preparations were enrolled. Composite events including all-cause mortality, IS hospitalization, and myocardial infarction-related hospitalization in the follow-up period under therapy with MgSt-ASA or non-MgSt-ASA preparations were considered primary outcomes. Hazard ratios (HRs) were adjusted with the baseline comorbidities and medications using the Cox model. RESULTS A total of 19 500 patients with IS (60% males, average age 67 years) were identified, which included 2064 patients receiving MgSt-ASA treatment initially and 17 436 patients receiving non-MgSt-ASA preparation initially. The crude incidence of composite events was 11.65 per 100 person-years, whereas it was 11.45 and 13.90 per 100 person-years for patients receiving non-MgSt-ASA and MgSt-ASA treatments, respectively. The risk of composite events was higher in patients receiving MgSt-ASA preparations than in those receiving non-MgSt-ASA formulations, with the adjusted HR being 1.23 at 95% confidence interval of 1.02 to 1.47. CONCLUSIONS MgSt-ASA preparation use was associated with a higher risk of composite events than non-MgSt-ASA preparations. Review of aspirin formulations under regulatory intervention is warranted.