Aspirin resistant patients are at a greater risk of clinically important adverse cardiovascular events, indicating that such resistance is a biological entity that should be considered when recommending aspirin as antiplatelet therapy, according to researchers from Toronto General Hospital.

George Krasopoulos, MD, cardiovascular surgery fellow, and colleagues culled databases from 1966 to the present. They published results in the Jan 17 issue of the British Medical Journal.

They identified 20 studies totaling 2,930 patients with cardiovascular disease. Most studies used aspirin regimens ranging from 75 mg to 325 mg daily, and six studies included adjunct antiplatelet therapy. Compliance was confirmed directly in 14 studies and by telephone or interviews in three.

Overall, the researchers found that 28 percent of patients were classified as aspirin resistant. A cardiovascular related event occurred in 41 percent of patients, death in 5.7 percent, and an acute coronary syndrome in 39.4 percent.

Aspirin resistance was less prevalent in men than in women and higher in patients with previous renal impairment.

Platelet inhibitors such as clopidogrel and tirofiban did not provide any benefit to aspirin resistant patients.