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Aspirin Resistance

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Dr Penny Bernstein - MBBCh(WITS), FC Path(Haem) SA (in colaboration with other authors).

PATHCHAT NO 15: ASPIRIN RESISTANCE

The full article was recently published in the Journal of the Neurological Sciences 277 (2009) 80-82. Journal homepage: www.elsevier.com/locate/jns Below is the shortened version.

INTRODUCTION

Stroke is one of the leading causes of death, both in the developed and developing world. In the USA, stroke is the third leading cause of death (after heart disease and then cancer) and the leading cause of chronic disability.^1,2 Stroke exacts a draining financial, as well as social burden on society, incurring costs of up to R30 billion per year (or approximately R50 000 per patient).

In a recent study of the ocurrence of secondary ischaemic events among those with cardiovascular disease, it was found that 11.8% of the cohort with an initial stroke presented with a secondary ischaemic cardiovascular event within 3 years. More than 75% of these secondary events were recurrent strokes.

In South Africa, stroke is estimated to cause between 8 to 10% of all reported deaths.W hile HIV is changing the mortality statistics in subSaharan Africa, cardiovascular disease remains a leading cause of death in most population groups and has a severe impact on the South African economy.HIV on its own also contributes to the risk of a stroke.  A cornerstone in the prevention of ischaemic events is aspirin (acetylsalicylic acid) therapy which has been shown to cause a 25% reduction in death, myocardial infarction and stroke in high-risk vascular patients. ⁸ However, it appears that aspirin's antiplatelet effect is not uniform in all patients, with some patients experiencing aspirin resistance. This is demonstrated by patients who experience secondary thrombotic or embolic vascular events while on therapeutic doses of aspirin.  Previous studies have estimated that between 8 and 45% of studied populations are aspirin resistant. A laboratory test to diagnose aspirin resistance would be beneficial to the clinician in deciding on optimal antiplatelet therapy for a particular patient. Aspirin resistant patients should be offered newer antiplatelet agents, such as clopidogrel, or a combination of aspirin with clopidogrel.  Platelet aggregation and sensitivity assays have been studied as indicators of aspirin resistance. However, different studies have used different definitions of the term “aspirin resistance” , and there is still a paucity of confirmatory data showing that those patients diagnosed “aspirin resistant” by laboratory investigations are the ones who will be more likely to restroke.

A clinical definition of aspirin resistance could be phrased as follows:

-the failure of the compound to protect the patient from an ischaemic event despite regular intake of appropriate doses. However, functional or biochemical in vitro tests would be best in order to individualise antiplatelet therapy in patients at risk of thrombotic complications, for example, for the secondary prevention of a Cerebrovascular Accident (CVA) or Transient Ischaemic Attack (TIA).

The study objective was to determine the prevalence of aspirin resistance and/or platelet hypersensitivity as determined by platelet aggregometry in Caucasian patients who have suffered one or more CVAs and/or TIAs as compared with controls.

 

Read the full article here.