The quality of evidence is downgraded by suspected publication bias.
A Cochrane review [Abstract] 1 included 15 studies with a total of 33 970 subjects. Randomised controlled trials comparing over 30 days use of aspirin plus clopidogrel with aspirin plus placebo or aspirin alone in people with coronary disease, ischaemic cerebrovascular disease, peripheral arterial disease, or at high risk of atherothrombotic disease were included. Studies including only people with coronary drug-eluting stent (DES) or non-DES, or both were excluded.
There was no difference in cardiovascular mortality (RR 0.98, 95% CI 0.88 to 1.10; 7 studies, n=31 903) or all-cause mortality (RR 1.05, 95% CI 0.87 to 1.25; 9 studies, n=32 908) when aspirin plus clopidogrel was compared to aspirin alone.Clopidogrel plus aspirin was associated with a reduced risk of fatal and non-fatal myocardial infarction (RR 0.78, 95% CI 0.69 to 0.90; 6 studies, n=16 175) and of fatal and non-fatal ischaemic stroke (RR 0.73, 95% CI 0.59 to 0.91; 5 studies, n=4 006) compared with aspirin alone.
Clopidogrel plus aspirin increased the risk of major bleeding (RR 1.44, 95% CI 1.25 to 1.64; 10 studies, n=33 300) and of minor bleeding (RR 2.03, 95% CI 1.75 to 2.36; 8 studies, n=14 731) compared with aspirin plus placebo or aspirin alone.
Comment: In acute non-ST coronary syndrome, it is unclear whether the beneficial effect is largely due to the administration of the combination therapy early after the acute event or whether the beneficial effect is consistent and relevant in the long term. There is no evidence of a net benefit on routinely adding clopidogrel to standard aspirin therapy for preventing cardiovascular events in people at high risk of cardiovascular disease and in people with established cardiovascular disease without a coronary stent.
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