Six RCTs were included (n=7,648, patients range 36 to 3,299). Four trials were considered high-quality. Four trials had concealed treatment allocation and blinded outcome assessment. One trial did not conceal treatment allocation, but did have blinded outcome assessment. One trial failed both criteria.
Compared with aspirin alone, aspirin plus dipyridamole yielded a significant reduction in the overall risk for stroke (RR 0.77, 95% CI 0.67 to 0.89; six RCTs) and the composite outcome of nonfatal stroke, nonfatal myocardial infarction and vascular death (RR 0.85, 95% CI 0.76 to 0.94; five RCTs). Heterogeneity was absent for these comparisons. Analyses restricted to high quality trials (four RCTs) showed very similar results.
Compared with aspirin alone, trials using predominantly extended-release dipyridamole showed a statistically significant reduction in the overall risk for stroke (RR 0.76, 95% CI 0.65 to 0.89; two RCTs) and the composite outcome (RR 0.82, 95% CI 0.73 to 0.92; two RCTs). Heterogeneity was absent for these comparisons.
For trials using immediate-release dipyridamole, there was no significant reduction in risk for stroke (four RCTs) or the composite outcome (three RCTs).