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Being resistant to aspirin makes patients four times more likely to suffer a heart attack or stroke or even die from a pre-existing heart condition, a study has found.
The research, led by Professor Michael Buchanan of McMaster University Health Sciences Centre, Canada, and just published online in the British Medical Journal, relates to patients who are prescribed aspirin long-term as a way of preventing clots from forming in the blood.
Patients labelled “aspirin-resistant” have platelets that are not affected in the same way as those of patients responsive to the drug, ie people who are “aspirin-sensitive”.
There is currently no agreed method of accurately determining who is and is not aspirin-resistant and the reasons why someone might be so are a cause of controversy.
Relatively few studies have looked at whether aspirin resistance has any impact on clinical outcome, so the Canadian researchers undertook a review of all available data to better understand the relationship between the two.
They identified 20 studies, involving 2,930 patients with cardiovascular disease, all of whom had been prescribed aspirin as a way of preventing clots from forming in the blood. Of these, 28% were classified as aspirin-resistant.
They found that all aspirin-resistant patients, regardless of underlying clinical condition, were at greater risk of suffering a heart attack, stroke or even dying.
In particular, they found that 39% of aspirin-resistant patients compared to 16% of aspirin-sensitive patients suffered some sort of cardiovascular event.
They also found that taking other drugs to thin the blood, such as clopidogrel or tirofiban, did not provide any benefit to these patients.
The authors conclude that further studies are needed on aspirin resistance to identify the most useful test to determine the condition.
They also say aspirin resistance “is a biological entity that should be considered when recommending aspirin as antiplatelet therapy”.