Is Aspirin Resistance A True Entity?

Aspirin

Aspirin has been a recognized agent to inhibit platelet function and prevent clotting.  We use it to prevent heart attacks and strokes. It’s used in individuals who have a transient ischemic attack or mini-stroke to prevent a future major stroke. It’s also used as a component of the therapy in patients who have stents put in arteries to relieve arterial blockages.

Despite the use of the aspirin, either alone or in concert with other medications, a certain percentage of patients do have the heart attack or stroke we are hoping to avoid. Scientists have postulated that a number of these patients have a condition called aspirin resistance. They believe aspirin may not work in them due to genetic factors that affect the way aspirin works. The belief is so strong that certain labs now offer genetic assays to assess whether you are a patient with aspirin resistance.

Garret A. FitzGerald, MD, and associates from the University of Pennsylvania published their research in the online section of Circulation: Journal of the American Heart Association which questions the existence of aspirin resistance at all. They recruited 400 healthy non-smoking participants between the ages of 18- 55 to measure the response to the ingestion of a traditional 325 mg regular aspirin or an enteric coated version.  They were able to use several different well accepted measures of aspirins anti-platelet effects to divide the group into aspirin responders and non-responders. They basically found that the non-responders were primarily individuals who received enteric coated aspirin. When you tested their blood in the laboratory with regular non-coated aspirin, or tested them with non-coated aspirin, they suddenly became responders.  FitzGerald and colleagues concluded that “pseudo resistance is caused by delayed and reduced absorption of coated aspirins.”

Doctors and pharmacists have encouraged the use of “coated” aspirin to offset aspirin’s tendency to irritate the lining of the stomach and duodenum and initiate gastrointestinal bleeding. Based on this paper it seems reasonable to suggest to patients that they use regular uncoated aspirin to achieve the desired anti-platelet effect if the patient is not high risk for intestinal bleeding.

 

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