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Title: Aspirin resistance : prevalence and mechanism
Author: Halawani, Saeed H. M.
ISNI:       0000 0004 2709 561X
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2010
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Aspirin is the most commonly used antiplatelet drug in the secondary prevention of cardiovascular events. Many patients experience thromboembolic events despite daily aspirin therapy. On the basis of clinical and laboratory findings, an issue of concern has emerged, frequently referred to as “aspirin resistance”. The aim of this thesis was to establish the prevalence of laboratory aspirin resistance in patient populations and to elucidate the reasons for aspirin failure. The thesis comprises two independent studies in which I assessed a range of clinical and laboratory measures in patients with peripheral arterial disease (PAD) and patients with acute ischaemic stroke. The effect of in-hospital aspirin administration on platelet response was determined in acute stroke patients. Laboratory tests for platelet and aspirin response were compared with the current gold standard assay of optical platelet aggregometry with arachidonic acid. A cut-off value for definition of incomplete response to aspirin was determined. The current literature is reviewed and discussed. Incomplete aspirin response was found in 18% of aspirin-treated patients with PAD. There were no significant differences in any of the measured markers nor in clinical parameters between responders and incomplete responders. The prevalence of incomplete aspirin response in acute ischaemic stroke or TIA was 43%. However, after observed aspirin administration in hospital, this percentage decreased to 29%, suggesting incomplete compliance in some patients. On admission, platelets from patients with incomplete response were significantly more sensitive to adenosine diphosphate (ADP) when compared with those from responders. There were no other differences that characterised the incomplete responders to aspirin. The data support the growing body of opinion that true biochemical resistance to aspirin is uncommon. Incomplete adherence to therapy was found to be a major cause of incomplete response to aspirin and therefore amenable to intervention. The problem remains of which laboratory methods should be employed as no single test has emerged as clinically informative.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Aspirin