Prevalence of aspirin resistance measured by PFA-100.
BACKGROUND
Aspirin protects from cardiovascular events. However, a number of patients who take this drug suffer events, probably due to aspirin resistance. Our objective was to determine the prevalence of aspirin resistance in patients taking this drug and to test if resistance is related to different variables.


METHODS
Platelet function was studied in 113 patients (90 men) aged 63+/-9 (80 with stable ischaemic heart disease) who took aspirin (100 to 300 mg/day). By a platelet function analyzer, called PFA-100, the epinephrine closure time was studied. We also analysed the possible relationship between epinephrine closure time and the following variables: total cholesterol, LDL, HDL cholesterol, total/HDL cholesterol, triglycerides, lipoprotein(a), and C reactive protein. The possible association between aspirin resistance (epinephrine closure time <161 s) and different variables was also analyzed with the SPSS statistical package. Results are expressed in median (interquartile range).


RESULTS
Aspirin resistance was found in 32% of cases. Ischaemic heart disease, smoking habit, and treatment with statins were associated with a significantly greater percent of resistance (p=0.049, 0.009, and 0.043, respectively). Patients with aspirin resistance had higher levels of total/HDL cholesterol: 4.46 (3.76-5.55) vs. 3.97 (3.20-4.75) (p = 0.023); and lipoprotein(a): 57.2 (24.8-85.0) mg/dl vs. 13.1 (3.7-38.0) mg/dl (p = 0.007).


CONCLUSIONS
Aspirin resistance is frequent and easily detected by PFA-100. It occurs more frequently in smokers. A mild association is found with ischaemic heart disease, some lipids, and treatment with statins. Our results support the applicability of this method to clinical practice.
Coma-Canella
Isabel
I
Department of Cardiology and Cardiovascular Surgery, Facultad de Medicina, Clínica Universitaria de Navarra, Avenida de Pio XII, 36. 31008 Pamplona, Spain. icoma@unav.es
Velasco
Amelia
A
Castano
Sara
S
D000368:Aged; D001241:Aspirin / Q000494:pharmacology* / Q000627:therapeutic use; D002545:Brain Ischemia / Q000517:prevention & control; D003430:Cross-Sectional Studies; D004351:Drug Resistance; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000517:prevention & control; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D010979:Platelet Function Tests; D015995:Prevalence; D013997:Time Factors
D010975:Platelet Aggregation Inhibitors; D001241:Aspirin