Introduction: Antiplatelet resistance is one of the urgent issues in current stroke care. One-third to one-half of the patients who experience a recurrent stroke is already on antiplatelet medications. We studied resistance to aspirin and clopidogrel in Indian stroke patients and its association with gene polymorphisms.
Methods: Platelet function testing by light transmission aggregometry was performed on 65 patients with ischemic stroke who were stable on dual antiplatelet therapy (clopidogrel 75 mg OD and aspirin 75 mg OD) along with 65 age-matched controls. Aspirin resistance was considered as mean platelet aggregation ≥70% with 10 μM adenosine diphosphate (ADP) and ≥20% with 0.75 mM arachidonic acid. Clopidogrel resistance was defined as <10% decrease from the baseline in platelet aggregation in response to ADP 10 μM and semi-response as <30% decrease from the baseline. Polymorphisms CYP2C19 * 2 and GPIIb/IIIa (PLA1/A2) were genotyped by polymerase chain reaction-restriction fragment length polymorphism.
Results: We found 64.6% (42/65) patients with inadequate response to clopidogrel (15.4% [10/65] resistant and 49.2% [32/65] semi-responders) and 4.6% (3/65) patients with inadequate response to aspirin (3.1% [2/65] resistant and 1.5% [1/65] semi-responder). The frequency of CYP2C19*2 mutant genotype was significantly higher in clopidogrel nonresponders compared to responders (P = 0.014). Clopidogrel nonresponsiveness was much higher in small vessel stroke.
Conclusion: Unlike aspirin, a high proportion of nonresponders to clopidogrel was identified. In an interim analysis on 65 Indian patients, a significant association was found between CYP2C19*2 and clopidogrel nonresponsiveness.
Keywords: Antiplatelet resistance; aspirin; clopidogrel; gene polymorphism; ischemic stroke.