Eight RCTs were included in the review (n=91,744). All were of high quality.
Combined therapy versus aspirin monotherapy in patients with acute coronary syndrome (three RCTs):
Combined therapy significantly reduced the odds of a major coronary event or fatal/non-fatal myocardial infarction (OR 0.85, 95% CI: 0.77, 0.94, p=0.002, NNT=67) or fatal/non-fatal myocardial infarction (OR 0.81, 95% CI: 0.74, 0.89). There was significant heterogeneity in the results for major bleeding (p=0.001). There was no significant difference between the groups for all-cause mortality or major bleeding.
Combined therapy versus aspirin monotherapy in patients with percutaneous coronary intervention (three RCTs):
Combined therapy significantly reduced the odds of a major coronary event (OR 0.66, 95% CI: 0.56, 0.78, p=0.002, NNT=9) or fatal/non-fatal myocardial infarction (OR 0.81, 95% CI: 0.74, 0.89). There was no significant difference between the groups for all-cause mortality or major bleeding.
Combined therapy versus monotherapy in patients with other conditions (two RCTs):
There was no statistically significant difference between the groups for efficacy outcomes, but combined therapy significantly increased the odds of major bleeding compared with either clopidogrel (OR 3.37, 95% CI: 2.09, 5.44; one RCT) or aspirin (OR 1.64, 95% CI: 1.27, 2.10; one RCT) monotherapy.
Subgroup analyses:
When studies were subgrouped by duration of follow up, the odds of major bleeding were significantly increased in longer studies (OR 1.80, 95% CI: 1.41, 2.30, p<0.00001; five RCTS, duration eight to 28 months), but not in shorter studies (two RCTS, duration 30 days or less).