The second European Stroke Prevention Study (ESPS-2) recently reported a substantial benefit of dipyridamole combined with aspirin over aspirin alone in the prevention of stroke. This appears to be at odds with previous studies suggesting that dipyridamole adds nothing to aspirin alone.
To review and compare the results of ESPS-2 and previous studies of dipyridamole plus aspirin and aggregate them in a meta-analysis.
We combined the detailed data provided by the Antiplatelet Trialists' Collaboration on the previous studies of dipyridamole plus aspirin with the results from ESPS-2. The data on the previous trials were listed in the appendix of the 1994 publication of the Antiplatelet Trialists' Collaboration.
The results of our meta-analysis demonstrate that for the outcome of nonfatal stroke, ESPS-2 overwhelms previous data, which, even in the aggregate, did not include enough patients or outcome events to exclude efficacy for the combination of dipyridamole and aspirin. Differences between ESPS-2 and previous studies, which may have contributed to different results, include the doses and preparations of aspirin and dipyridamole.
The ESPS-2 showed that dipyridamole alone prevents stroke. More importantly, it showed a substantial benefit for dipyridamole combined with aspirin over aspirin alone. When the ESPS-2 data are aggregated with the 14 previous trials of dipyridamole combined with aspirin over aspirin alone, the combination reduces the risk of stroke by 23% over aspirin alone. Nevertheless, important questions remain unanswered. We conclude that another randomized clinical trial showing a significant benefit of the combination of dipyridamole plus aspirin over aspirin alone may be needed before the addition of dipyridamole to aspirin is widely accepted for prevention of stroke.