Resistance to the antiplatelet action of aspirin is associated with a four-fold increase in major adverse events such as myocardial infarction and ischemic stroke, according to an article published online January 17 by BMJ.

According to background information in the article, there is currently no universal method of accurately determining who is and who is not aspirin resistant; further more, the basis of aspirin resistance is currently a cause of controversy.

Relatively few studies have examined whether aspirin resistance has any impact on clinical outcome, so in the current study Canadian researchers carried out 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 means of preventing thrombosis. Of the total, 28 percent were classified as aspirin resistant.

They found that all aspirin-resistant patients, regardless of underlying clinical condition, were at greater risk for a myocardial infarction, stroke or death. In particular they found that 39 percent of aspirin-resistant patients compared with 16 percent of aspirin-sensitive patients had 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 the aspirin-resistant patients.

The authors concluded that there needs to be further studies on aspirin resistance to identify the most useful test to determine the condition. They also noted that aspirin resistance "is a biological entity that should be considered when recommending aspirin as antiplatelet therapy."