Dipyridamole trials in stroke prevention.

Research on the benefits of aspirin combined with other antiplatelet regimens for stroke prevention has yielded inconclusive results. Early trials of aspirin plus dipyridamole (DP) were unable to detect a significant benefit for combination therapy over aspirin alone, although they clearly demonstrated the value of combination therapy compared with placebo. Early trials such as the AICLA (Accidents ischémiques cérébraux liés a l'athérosclérose) trial and the American-Canadian Cooperative Study lacked the statistical power to detect differences in the benefit of combination versus monotherapy because of the small number of events in each treatment group. The Antiplatelet Collaboration, in its meta-analysis published in 1994, also failed to detect a significant difference between the benefit of aspirin plus DP and that of aspirin alone for the combined end point of stroke, myocardial infarction, and vascular death. The large European Stroke Prevention Study 2 (ESPS-2) trial recently provided evidence that aspirin plus DP does lead to a significantly greater reduction than aspirin alone. The 6,602 patient trial randomized patients into four treatment groups: aspirin (50 mg daily) plus sustained-release DP (400 mg daily), aspirin alone, DP alone, or placebo. The trial found that low-dose aspirin plus DP more than doubled the reduction in stroke risk achieved with aspirin alone, a 37% risk reduction for the combination versus 18.1% for aspirin alone. The results also suggest that the effects of aspirin and DP are additive.