Resistance to low-dose aspirin therapy among patients with acute coronary syndrome in relation to associated risk factors
Journal of Clinical Pharmacy and Therapeutics, 05/04/2012Salama MM et al.
There is inter–individual variability in response to the antiplatelet effect of standard doses of aspirin (150, 300 mg/day). The response to aspirin 300 mg/day is enhanced in resistant patients when compared to 150 mg/day. There was a significant association between aspirin resistance and atherothrombotic risk factors (diabetes, hyperlipidaemia and obesity).
The antiplatelet effect of 150 mg/day aspirin was studied prospectively in 50 consecutive patients with unstable angina or non–ST–segment elevation myocardial infarction.
Platelet aggregation was measured using optical platelet aggregometry and serum thromboxane B2 level.
Aspirin resistance was defined as collagen (1 μg/mL) and adenosine diphosphate (ADP) (5 μmol/L)–induced platelet aggregation of ≥40% when compared with control values.
Twenty healthy age– and sex–matched individuals were taken as a control group.
All patients were subjected to complete medical history (risk factors, medications), thorough clinical examination, ECG, coronary angiography and laboratory investigations including: complete haemogram, coagulation, kidney, liver and lipid profiles, fasting blood glucose and glycated haemoglobin (HbA1C).
Eleven of 50 patients (22%) were found to be aspirin resistant.
A highly significant difference was found between the mean values of ADP, collagen–induced platelet aggregation percentage and thromboxane B2 level after aspirin 150 mg/day when compared with the corresponding mean values after aspirin 300 mg/day among the resistant patients (66 ± 7•01%, 62 ± 4•34% and 620 ± 64•58 pg/mL, respectively, vs. 26•87 ± 2•85%, 16•5 ± 3•8% and 77 ± 11•3 pg/mL) indicating enhanced response to aspirin after escalating the dose.
The presence of atherothrombotic risk factors (hypertension, smoking, family history of ischaemic heart disease and previous MI) were not statistically different between aspirin–resistant and aspirin–sensitive patients.
However, there was a highly significant difference between the aspirin sensitive and the resistant patients regarding the other risk factors (diabetes mellitus and dyslipidaemia) (P < 0•01).
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