Coronary heart disease is the single leading cause of death in the Western world. Aspirin is a fundamental part of the prevention and treatment of coronary heart disease and is used by millions of patients worldwide.
Most coronary heart disease deaths are caused by platelets sticking together and forming blood clots (thrombosis) that block blood flow within heart arteries and result in heart attacks. By inhibiting thrombosis, aspirin keeps platelets from sticking together by specifically blocking an important enzyme, COX-1, within the platelet.
Recent studies suggest that there may be a small group of patients who are resistant to the effects of aspirin. The definition of aspirin resistance is the failure of aspirin to block its intended target, COX-1. These latest findings demonstrate that aspirin resistance is rare at all doses (81-325mg daily doses) in patients with coronary artery disease when it is measured by methods that specifically indicate the level of COX-1 inhibition.
One hundred and ten patients with a history of coronary artery disease treated with aspirin were studied. All patients were randomly placed on 81mg, 162mg and 325mg of aspirin daily for four weeks each for a total of twelve weeks. Then, response to aspirin was tested by eight different methods. When methods were used that directly indicated the ability of aspirin to block its target, COX-1, it was found to be highly effective. Aspirin resistance was only observed in 1-5% of patients. However, when we used less direct methods to indicate the blockade of COX-1, we found that up to 30% of patients displayed resistance to at least one dose.