Platelet function analysis with two different doses of aspirin

Objectives: We aimed to compare the level of platelet inhibition using the platelet function analyzer (PFA)-100 in patients receiving low and medium doses of aspirin.
Study design: On a prospective basis, 159 cardiology outpatients (83 men, 76 women; mean age 60.9±9.9 years) taking 100 mg/day or 300 mg/day aspirin at least for the previous 15 days were included. Of these, 79 patients (50%) were on 100 mg and 80 patients (50.3%) were on 300 mg aspirin treatment. Blood samples were collected between 09: 30 and 11: 00 hours in the morning. Platelet reactivity was measured with the PFA-100 system. Incomplete platelet inhibition was defined as a normal collagen/epinephrine closure time (<165 sec) despite aspirin treatment.
Results: Baseline clinical and laboratory characteristics of the patient groups taking 100 mg or 300 mg aspirin were similar. The overall prevalence of incomplete platelet inhibition was 22% (35 patients). The prevalence of incomplete platelet inhibition was significantly higher in patients treated with 100 mg of aspirin (n=24/79, 30.4%) compared with those treated with 300 mg of aspirin (n=11/80, 13.8%) (p=0.013). In univariate analysis, female sex (p=0.002) and aspirin dose (p=0.013) were significantly correlated with incomplete platelet inhibition. In multivariate analysis, female sex (OR: 0.99; 95% CI 0.9913-0.9994; p=0.025) and aspirin dose (OR: 3.38; 95% CI 1.4774-7.7469; p=0.003) were found as independent factors predictive of incomplete platelet inhibition.
Conclusion: Our findings suggest that treatment with higher doses of aspirin can reduce incomplete platelet inhibition especially in female patients.

Keywords: Aspirin/therapeutic use, blood platelets/drug effects, dose-response relationship, drug; drug resistance; platelet aggregation/drug effects; platelet function tests/methods