Dipyridamole

Trials using other antiplatelet agents, such as sulfinpyrazone and suloctidil, have not been as effective as aspirin or have not demonstrated any added benefit to aspirin alone. Dipyridamole was not thought to have any added benefit to aspirin based on the French AICLA trial, however results from the European Stroke Prevention Stroke Study II have indicated that 200 mg BID of modified-release Dipyridamole was more effective than Aspirin (25 mg BID) in the prevention of stroke, myocardial infarction and vascular death after TIA or minor stroke. In this trial 6602 patients were randomized in a factorial design, 76% with stroke and 24% with TIAs. Primary endpoints were stroke, death, and stroke or death together. Patients were followed for 2 years. The relative risk reduction of stroke was 18% for aspirin, 16% for dipyridamole, and 37% for the combination of the two. The relative risk reduction of stroke or death was 13% for aspirin, 15% for dipyridamole, and 24% for the combination of the two. Factorial analysis also demonstrated a highly significant effect of ASA and dipyridamole for preventing TIA. Headache was the most common adverse event and occurred more frequently in the dipyridamole group. Bleeding and GI hemorrhage was more common in patients taking ASA compared to placebo or dipyridamole. The combined long-acting formulation is not yet available or approved in the U.S.
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Clopidogrel

Clopidogrel, a thienopyridine derivative similar to ticlopidine, is a new antiplatelet agent which is an inhibitor of platelet aggregation induced by adenosine diphosphate. This agent at a dose of 75 mg BID was recently compared to aspirin (325 mg per day) in reducing the risk of ischemic stroke, myocardial infarction, or vascular death among patients with atherosclerotic vascular disease. Nearly 20,000 patients with stroke, MI, or peripheral vascular disease were recruited over 3 years with a mean follow-up of 1.9 years. Patients treated with clopidogrel had a 5.32% risk of stroke, MI, or vascular death compared to 5.83% with ASA (p=.043). Among the stroke subgroup, there was a nonsignificant reduction from 7.71% to 7.15% in outcome events, however the number of non-fatal strokes were reduced from 322 to 298 with clopidogrel. The most significant effects were observed for the subgroup with PAD. Among patients with PAD or stroke with a prior history of MI, the event rate reduced from 10.74% to 8.35% with clopidogrel (relative risk reduction of 22.7%). The medicine was safe and was not associated with an increased risk of neutropenia. The drug is now FDA approved.

Aspirin

Numerous clinical trials have been done comparing aspirin with placebo for the prevention of stroke and death after TIA or minor stroke.The Antiplatelet Trialist Collaboration Group have used meta analyses to combine the results of these various antiplatelet studies in which ASA was the most widely used agent. In their most recent analyses of 17 trials among persons with a past history of stroke or TIA, they reported an odds reduction of 22% for non-fatal stroke, non-fatal MI or vascular death with a 2-year risk of 18% for those treated with antiplatelets and 22% for controls. Few of the individual aspirin studies were directed at the efficacy of aspirin in preventing recurrent stroke after an established stroke. In the meta-analyses among those with a completed stroke, the odds reduction was 16% for non-fatal stroke, non-fatal MI or vascular death. Individual aspirin studies have sometimes failed to find a beneficial effect for women. However, in the meta-analyses similar reductions were found for women and men, young and old, hypertensives and normotensives and diabetics and non-diabetics.
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The issue of the dose of aspirin needed to prevent stroke is still controversial. Recommendations range from a low of 30 mg per day to a high of 1300 mg per day. The data for the efficacy of stroke prevention for lower doses is available only from trials involving patients with TIA and minor stroke. Gastrointestinal hemorrhage and other aspirin-related side effects are clearly reduced with the lower doses. The Antiplatelet Trialist’s Collaboration Report cited three trials using doses of 300-325 daily and compared the outcome for major vascular events, including stroke, to the 15 trials using 900-1500 daily. Cheap generic lipitor. The authors concluded “…the studies of 300-325 mg/day appeared to have yielded results that were at least as good as those yielded by 900-1500 mg/day.” However, a review of stroke trials found that the risk reductions were not as great with the low dose aspirin programs compared to the higher dose programs. They stated that this “raised the possibility that 325 mg/day or less of aspirin may not be equally effective as 975 mg/day or more.” The data from aspirin trials suggest that a dose of aspirin as low as 325 mg is better tolerated and might prove as effective as the higher doses of 1000-1300 mg. In 2006, the US Food and Drug Administration revised their recommendations to endorse 50-325 mg of ASA per day as the standard dose to prevent stroke in TIA and stroke survivors.