DSI Newsletter: Aspirin Resistance

DSI Newsletters, Issue 41:
Aspirin Resistance

Heart attack risk jumps as aspirin sensitivity lost
For the first time, researchers have discovered that people with heart disease who are resistant to the blood-thinning effects of aspirin are at higher risk of death or a heart attack compared with those most sensitive to the drug.
The findings suggest that some patients with aspirin resistance may benefit from other drugs that have similar blood-thinning functions, the researchers report this week in the advance online edition of the April 9th issue of Circulation: Journal of the American Heart Association. Doctors have known for some time that some patients are less sensitive to the effects of aspirin than others.
"It is important to remember that aspirin remains an important and highly effective treatment and should be continued in all at-risk patients," said Dr. John W. Eikelboom, of Royal Perth Hospital in Australia. "What our results indicate is that we can do better than aspirin alone," Eikelboom told Reuters Health.
Combinations of drugs might be advisable, he explained.
"One such example is: clopidogrel (Plavix), which is now proven to be effective in combination with aspirin in patients with unstable angina." Unstable angina is chest pain, often severe, that develops suddenly and recurs over days or weeks, even at rest. It is associated with a high risk of heart attack. Another is: aspirin/extended-release dipyridamole (Aggrenox).
In a new study, Eikelboom and colleagues compared 488 aspirin-taking patients who had a heart attack, stroke or died during a five-year period with 488 aspirin-taking patients who did not have a heart attack or other problem during the same time.
The researchers conducted urine tests to measure a substance related to thromboxane A2, a chemical that boosts the "stickiness" of platelets. Platelets are a type of cell that plays a key role in blood clot formation; when platelets stick together they can form blood clots that can lead to a heart attack or stroke.
People who are on aspirin therapy but still have a high level of thromboxane A2 in their blood can be considered aspirin resistant. Thromboxane A2 is difficult to measure directly, but one of its byproducts can be measured in urine.
Aspirin-resistant patients — those with the highest levels of thromboxane A2 — had double the risk of a heart attack compared with patients who had the lowest levels, Eikelboom's group determined. Furthermore, the aspirin- resistant patients were 3.5 times more likely to die from heart disease.
The results held true even after the researchers accounted for other risk factors such as high blood pressure and smoking.
The risk of stroke was not any higher in aspirin-resistant patients, but this was probably "a play of chance," the researchers say. They point out that a fairly small number of patients had strokes, which probably affected the research team's ability to show a statistical relationship between strokes and aspirin resistance.
The findings suggest that urine tests for the thromboxane byproduct could one day help determine those heart disease patients who might benefit from medication in addition to aspirin, the authors conclude.
Eikelboom notes that while such tests are available, patients should not ask their doctors to test their thromboxane level.
"The test is commercially available but is still a research tool," he said.
So, in conclusion, adding a second class (type) of blood thinner may help prevent a heart attack or stroke. We need more clinical trials to determine if measuring this urinary byproduct of thromboxane A2 actually predicts aspirin resistance reliably and if Plavix or Aggrenox can help prevent any disease from occurring.

Sincerely:

Joseph Saponaro, MD, DABIM, FACP, CPI, CCI, CCRI, CCRC, CCRP
Board Certified Internist, JPMC
Principal Investigator, DSI
Diplomat American Board of Internal Medicine
Fellow American College of Physicians
Certified Physician Investigator by the AAPP
Certified Clinical Investigator by the DIA
Certified Clinical Research Investigator by the ACRP
Certified Clinical Research Coordinator by the ACRP
Certified Clinical Research Professional by SoCRA
Member: The American College of Preventive Medicine

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