Does prior use of antiplatelet therapy modify the effect of dual antiplatelet therapy in transient ischaemic attack/minor ischaemic stroke: A systematic review and meta-analysis

Background and purpose The purpose was to determine whether prior use of antiplatelet therapy modifies the effect of dual antiplatelet therapy in patients with acute minor ischaemic stroke or transient ischaemic attack. Methods A systematic review and meta-analysis of randomized controlled trials was performed comparing dual antiplatelet therapy to aspirin that reported subgroup analysis by prior antiplatelet use, adhering to the Cochrane Collaboration Guidelines. A fixed-effects meta-analysis was used to estimate a pooled treatment effect overall in subgroups with prior aspirin therapy and without prior aspirin therapy. Difference in treatment effect was assessed by testing p for interaction. The primary outcome measure was recurrent vascular events. Results Three eligible randomized controlled trials were identified, including 4831 participants with pre-existing antiplatelet use and 16,236 participants without pre-existing aspirin use. Recurrent vascular events occurred in 7.2% (95% confidence interval [CI] 4.3-10) of those without pre-existing aspirin use versus 7.3% (95% CI 4.1-10) of those receiving prior aspirin therapy. Effect of dual antiplatelet therapy on the primary outcome measure was consistent in participants with no prior aspirin use (odds ratio 0.75, 95% CI 0.66-0.84) compared to those taking aspirin before randomization (odds ratio 0.79, 95% CI 0.63-0.998) (p interaction = 0.66). The number needed to treat in the aspirin-naive group was 55 (95% CI 37 to -107) compared to 66 (95% CI 32-746) in those on prior aspirin therapy. Conclusions It was found that the effectiveness of dual antiplatelet therapy in patients with minor ischaemic stroke or high risk transient ischaemic attack does not significantly differ in patients with prior aspirin exposure; therefore there should be no influence on the decision to use dual antiplatelet therapy.