Prevalence of aspirin resistance in Asian-Indian patients with stable coronary artery disease.

Objective: To evaluate the prevalence of pharmacological resistance to aspirin therapy by measuring platelet functions using the technique of light transmission aggregometry.

Background: Aspirin is the cornerstone of antiplatelet therapy in patients with coronary artery disease (CAD). However, a substantial proportion of patients manifest breakthrough thrombotic events despite regular intake of aspirin suggesting therapeutic resistance to aspirin.

Methods: We prospectively studied 126 patients with stable coronary artery disease at a tertiary center, who were recruited after ensuring compliance with a single formulation of aspirin (enteric coated aspirin 150 mg). Platelet aggregation was measured using light transmission aggregometry with ADP (10 µM) and Arachidonic acid (0.5 mg/mL). Pharmacological aspirin resistance was defined as the combined demonstration of mean platelet aggregation of ≥70% with 10 µM ADP and a mean aggregation of ≥20% with 0.5 mg/mL A.A. Patients satisfying either one of the above criteria were defined as semi-responders. Patients satisfying neither criterion were defined as "aspirin responders".

Results: Out of 126 patients with stable CAD, 64 % were responders, 36% were non responders (semi-responders = 34% and resistant = 2%). Of the laboratory parameters, only the total leukocyte count was significantly associated with the presence of aspirin resistance (P < 0.03).

Conclusion: Pharmacological resistance to aspirin is noted in 36% (semi-responders = 34% and resistant = 2%) of Asian Indian patients with stable CAD. Long-term follow up of these patients will assist in determining the clinical importance of this phenomenon. © 2014 Wiley Periodicals, Inc.