Monday, October 30, 2006 Dumaguing: Aspirin resistance, fact or fable? By Dr. Vic Dumaguing To Your Health
CORONARY heart disease is the single leading cause of death in the Western world. 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 is a fundamental part of the prevention and treatment of coronary heart disease and is used by millions of patients worldwide. Aspirin keeps platelets from sticking together by specifically blocking an important enzyme, COX-1, within the platelet.
(But) recent studies suggested that there may be a group of patients who are resistant to the effects of aspirin. The definition of aspirin resistance in patients is the failure of aspirin to block its intended target, COX-1. The study demonstrates 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.
110 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 12 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, they found that it was highly effective. Aspirin resistance was only observed in one to five percent of patients. However, when they used less direct methods to indicate the blockade of COX-1, we found that up to 30 percent of patients displayed resistance to at least one dose.
The study is the largest thus far to compare multiple tests of aspirin's efficacy. The results strongly suggest that platelet aspirin resistance is overestimated by tests that do not directly reflect the level of aspirin's ability to block its target, COX-1. These results suggest that when measuring COX-1 inhibition with specific methods, aspirin is a very effective drug at all doses.
Dr. Paul Gurbel, director of Cardiology and Cardiovascular Research at the Sinai Hospital of Baltimore in Maryland and associate professor of medicine at the Johns Hopkins University School of Medicine, believes: "The occurrence of thrombosis in patients during aspirin therapy has been attributed to failure of the aspirin to block its target and is a pivotal topic in cardiovascular disease.
However, data suggests that aspirin blocks its target, COX-1, with high efficiency. Aspirin resistance has probably been overestimated by tests that do not take into consideration the activity of COX-1. Alternate reasons for the occurrence of thrombotic events in patients on aspirin therapy should be explored to further improve patient outcome".
Whatever is your dose, please take your aspirin on a full stomach.
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