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Resistance to aspirin has adverse effect on CVD outcomes

It is generally accepted that aspirin reduces total mortality and cardiovascular morbidity and mortality in both the primary and secondary prevention of cardiovascular disease. Aspirin is also cheap and generally safe. Unfortunately, it does not appear to be effective in everyone. This study assessed the impact of aspirin resistance on cardiovascular outcomes.

Data were analysed from 20 secondary prevention studies, involving a total of 2,930 patients who had been prescribed aspirin (75-325 mg/day) following acute coronary syndrome/MI, coronary revascularisation (PCI or CABG), stroke or other diagnosis of vascular disease. Each study used a platelet function assay to assess aspirin sensitivity. No one test was considered a gold standard as there is no consensus view at present.

The results showed that 28% of patients were classified as aspirin resistant. Unsurprisingly, a cardiovascular event occurred in 39% of the aspirin resistant patients compared with just 16% of the aspirin sensitive patients (OR 3.85, 95% CI 3.08-4.80, P=<0.001). There were also significantly higher rates of death, acute coronary syndrome, graft failure and new cerebral events in the aspirin resistant group.

Aspirin resistance was found to be significantly more common in women and those with renal failure.

Another interesting finding was that the increased risk seen in aspirin resistant patients was not ameliorated by the presence of another antiplatelet drug, such as clopidogrel or a glycoprotein IIb/IIIa inhibitor. This suggests that even targeting alternative platelet pathways is not necessarily effective in such patients.

These findings also mean that the true benefit of aspirin is likely to be even greater than current data suggest, as most studies have not taken aspirin resistance into account.

At present it is unclear what can be done about aspirin resistance, and whether it will turn out to be another nonmodifiable risk factor, like age and sex.

Krasopoulos G, Brister SJ, Beattie WS et al. Aspirin "resistance" and risk of cardiovascular morbidity: systematic review and meta-analysis BMJ 2008 doi: 10.1136/bmj.39430.529549.BE

Reviewer

Dr Peter Savill
GPwSI Cardiology, Southampton

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