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Senior Citizen Health & Medicine
Older Stroke, Heart Attack Victims Most Likely to
Benefit from Aspirin Therapy
Aspirin Failure leaving 20% of all ages unprotected
from second stroke, heart attack
 Feb.
26, 2008 It is well established in medical research that taking
aspirin will lower the risk of a second cerebrovascula event (stroke).
But new research has found that as many as one of five patients do not
have the antiplatelet response the protective effect that prevents
blood platelets from clogging arteries after taking aspirin.
"Millions of people use low-dose aspirin either for
prevention of a second stroke, second heart attack or second episode of
peripheral artery disease," said Francis M. Gengo, Pharm.D., lead
researcher on the University at Buffalo study.
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Gengo is professor of neurology in the UB School of
Medicine and Biomedical Sciences and professor of pharmacy practice in
the UB School of Pharmacy and Pharmaceutical Sciences.
"In those three indications, it's crystal clear
that aspirin reduces the risk of a second heart attack or stroke in most
patients. But we have known for years that in some stroke and heart
attack patients, aspirin has no preventive effect."
With no definitive data on the frequency of this
condition, known as aspirin resistance, physicians were left with a best
guess of between 5 and 50 percent, said Gengo.
UB researchers now have confirmed the 20 percent (1
in 5) figure through a strictly controlled study conducted over 29
months in 653 consecutive stroke patients seen at Dent Neurologic
Institute offices in the Buffalo suburbs Amherst and Orchard Park.
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Aspirin lowers the risk of a cardiovascular event
by preventing blood platelets from aggregating in the arteries and
obstructing blood flow. If blood drawn from a patient taking aspirin
shows that platelets are still aggregating, that patient is diagnosed as
being aspirin resistant. |
Results of the study were published Jan. 28 on the
Journal of Clinical Pharmacology's Web site as a "document of interest"
and will appear in a future issue of the journal.
Aspirin lowers the risk of a cardiovascular event
by preventing blood platelets from aggregating in the arteries and
obstructing blood flow. If blood drawn from a patient taking aspirin
shows that platelets are still aggregating, that patient is diagnosed as
being aspirin resistant. If a stroke patient has a second stroke while
on aspirin, the patient has experienced what is known as clinical
aspirin failure.
"We've known about clinical aspirin failure for
many years," said Gengo. "We're just beginning to understand clinical
aspirin resistance. The major question recently has been, 'If you are
aspirin resistant, does that mean you are more likely to be a clinical
aspirin failure? Is one related to the other?' The answer is, likely,
"yes."
"That's one of the critical pieces of information
provided by this paper," he said. "We looked at how frequently aspirin
resistance occurred in all patients and its prevalence in patients who
suffered clinical aspirin failure. What we found was, across the board,
about 80 percent of the patients in our study, were aspirin sensitive --
their platelets did not aggregate in arteries -- and 20 percent were
aspirin resistant.
"However, when we asked the same question of the
data from patients who had a second stroke while on aspirin [clinical
aspirin failures], 80 percent were aspirin resistant," said Gengo.
A large meta-analysis published nearly
simultaneously in the online version of the British Medical Journal
(BMJ) reached a similar finding. However, Gengo noted that while the BMJ
paper is a very important review, the UB/DENT study provides more
definitive information on the issue.
The number of patients was nearly six times larger
than in any of the individual studies included in the meta-analysis, he
said. "More importantly, all patients in the UB/DENT study had their
aspirin responder status confirmed, not once, but multiple times. And
lastly," he noted "it was determined objectively by urinanalysis that
all patients were actually taking their prescribed aspirin."
Of the 20 studies included in the BMJ
meta-analysis, compliance was confirmed by telephone or interviews in
three studies and was not able to be assessed in three more due to
insufficient information, according to the report.
In addition to quantifying the prevalence of
aspirin resistance and identifying the relationship between aspirin
resistance and clinical aspirin failure, the UB/DENT study provided
other data of clinical importance.
The researchers found that patients with coronary
artery disease are more likely to be aspirin resistant, as well as
patients with diabetes and those who suffered an earlier stroke, but not
a transient ischemic attack (TIA), known as a "mini-stroke."
However, they did not find a relationship between
aspirin resistance and hypertension or high cholesterol in their study
population. Gengo said this finding likely was due to the fact that
patients at the Dent Neurologic Institute are from an affluent suburban
population, and their hypertension and lipid levels tend to be extremely
well controlled.
Senior citizens get the most protection
The study also found that the younger the patient
when the first stoke or heart attack occurs, the higher the risk of
being aspirin resistant.
"You can think about that in a couple ways," noted
Gengo. "If you have a stroke when you're 50, you probably have much
worse vascular disease than the patient who has a stroke at 70, so you
are more likely to be aspirin resistant on that basis.
"Also, the younger you are the faster you turn your
platelets over," he said.
"If you are making platelets faster, you may need
more aspirin, and the faster you make them, the faster you're going to
overwhelm the aspirin. We don't really know for sure, but we speculate
the higher risk factor in our younger patients is based on one of those
two reasons."
The findings in the paper need to be confirmed in a
larger study population followed over 1-2 years, Gengo stated. In the
meantime, he suggested that clinicians could test a patient's
responsiveness to aspirin early on and prescribe accordingly.
Editor's Notes:
UB/Dent researchers who also contributed to the
study were Michelle Rainka, Pharm.D., UB adjunct instructor of pharmacy;
Alan Forrest, Pharm.D., UB professor of pharmacy, and Vernice Bates,
M.D., UB clinical associate professor of neurology. Additional
contributors from the Dent Neurologic Institute were research assistants
Matthew Robson and Michael Gengo, and Maurice Hourihane, M.D., an
attending physician.
The study was funded by the Dent Family Foundation.
The University at Buffalo is a premier
research-intensive public university, a flagship institution in the
State University of New York system and its largest and most
comprehensive campus. UB's more than 28,000 students pursue their
academic interests through more than 300 undergraduate, graduate and
professional degree programs. The School of Medicine and Biomedical
Sciences, School of Dental Medicine, School of Nursing, School of
Pharmacy and Pharmaceutical Sciences and School of Public Health and
Health Professions are the five schools that constitute UB's Academic
Health Center. Founded in 1846, the University at Buffalo is a member of
the Association of American Universities.
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