Gettysburg Medical News
 The Clinical View
 by P.E. Hoffsten, M.D.
16 March 2005

WHAT IS THE RIGHT DOSE OF ASPIRIN?

            In the 1930’s, a small town physician in Mississippi describing his belief that aspirin prevented heart attacks published paper.  That paper received little attention to almost 40 years later when John Vane demonstrated that aspirin prevented the activation of platelets.  He received a Nobel Prize for this work and soon thereafter studies began to test the hypothesis that aspirin might prevent heart attack and stroke.  To the present time, it is clearly demonstrated that aspirin is the cheapest and the most effective single step that a person can take to prevent heart attack and stroke in the long run.

            But arguments continue regarding the “right” dose of aspirin.  For years, aspirin came as a standard 5 grain (325 mg) aspirin tablet.  There was also “baby aspirin” that had 81 milligrams of aspirin in it.  One of the mysteries to this day is how aspirin may be involved in the development of a condition called Reye’s Syndrome.  This is a life-threatening condition that develops in babies treated with aspirin for febrile illness.  It is now strongly recommended that babies not receive aspirin to control fever.  Rather, Tylenol does appear to be safe and effective for this purpose.

            Aspirin sensitivity varies widely.  There are some people that are unable to take an aspirin a day without having gastric distress. There are other individuals who are able to take 20 aspirin per day to control rheumatoid arthritis and they seem to do remarkably well.  Until 1950, this was the only effective treatment that we had for rheumatoid arthritis.  The sensitivity and tolerably of aspirin varies quite dramatically in our population.  The question considered in this article is, “What is the right dose of aspirin?”  The very simple answer is that it is the dose that provides the desired protection with no side effects.  The question is raised because several studies have shown that some individuals who take aspirin on a regular basis get strokes or heart attacks anyway.

            The reason some individuals develop strokes or heart attacks, even while they are supposedly taking aspirin, fall into several possible explanations.  First of all, those that say they are taking aspirin, between 11-50% really are not taking the pill at all.  Studies have been done in which participants were asked if they were taking their aspirin on schedule.  A urine specimen was then checked to see if there was evidence of aspirin waste products in the urine.  Depending on the population, between 11-50% of the people who said that they were taking aspirin really weren’t.  People not taking their aspirin pill would have a real good reason why it wouldn’t work.

            It is known that products such as Ibuprofen (Motrin, Advil, Nuprin) interfere with aspirin’s antiplatelet effect.  Aspirin must attach to a certain place on a certain protein in order to be effective.  When a person uses Ibuprofen or Indocin, they interfere with aspirin’s ability to attach to the protein rendering the aspirin as ineffective in preventing strokes or heart attacks.  Regular use of Ibuprofen or Indocin is discouraged in people who use aspirin for stroke her heart attack prevention.  What role the recent controversy regarding Vioxx and Aleve has to do with its interference with aspirin effectiveness is not known.

            Just as there is a spectrum of blood pressures in our society, there is a substantial variation in the responsiveness to aspirin.  Previous work has indicated that approximately 80% of the population has an effective inhibition of platelet function thereby preventing heart attacks and strokes when given only 81 mg of aspirin daily.  Very close to 100% of the population has complete inhibition of platelet of function using 325 mg of aspirin daily.  When asked, I suggest that anyone who can tolerate the 325 mg aspirin tablet use that instead of the 81 mg low dose  aspirin.

            At this time, it is not practical to test individuals for aspirin resistance.  Several research studies are in process to see if an aspirin resistance test can be developed and whom it might be important for.

            In summary, for those that can tolerate 325 mg of aspirin daily, I think that this is the right dose.  If this causes side effects such as gastric irritation or asthma, or allergic reactions obviously, the medication should be avoided.  For those individuals who already have had one stroke or one heart attack,  studies now indicate that the use of aspirin along with the medication called clopidogrel (Plavix) is more effective than aspirin or Plavix alone in preventing a recurrent event.  The healthcare professionals at your local clinics are well versed in these considerations in helping an individual make the right decision on the right dose of aspirin for them.