clOpidogrel "resIstaNce" in a Selected Population of Patients at a Tertiary Cardiovascular Center in Trinidad

Clopidogrel, a second generation oral thienopyridine, remains an integral component of dual antiplatelet therapy (DAPT) in the management of cardiovascular disease (CVD) for almost two decades. Several studies underscore the importance of high on-treatment platelet reactivity (HPR) as a prognosticator for cardiovascular events including stent thrombosis. This phenomenon is often alluded to as "clopidogrel resistance" and yet to be clearly defined. Generally, it reflects the failure to achieve its antiaggregatory effect. Clopidogrel response is both complex and multifactorial, determined by a multitude of intrinsic and extrinsic mechanisms including genetic polymorphisms of the P2Y12 receptor, drug-drug interactions, and clinical factors such as suboptimal dosing regimens, acute coronary syndromes, diabetes mellitus, and possibly smoking.

High pre-treatment platelet reactivity may lead to mitigated clopidogrel-induced antiplatelet effects and are more commonly observed in specific clinical scenarios such as ACS, increased body mass index, and diabetes mellitus, in particular, insulin-dependent diabetes mellitus. Matetzky et al also surmised that nearly one-quarter of ST-segment elevation acute coronary syndrome patients would incur stent thrombosis due to this phenomenon.

Overall, HPR prevalence in various studies is estimated at 5%-44%, however, these are based on largely Caucasian populations and yet to be ascertained in a Caribbean subpopulation. Trinidad and Tobago has an ethnically diverse population with approximately one-third South Asian (Indo-Trinidadian), one-third Caribbean Black (Afro-Trinidadian) and the remaining one-third, mostly interracial and mixed. CVD is currently the leading cause of mortality in Trinidad and Tobago, accounting for up to 60% of all deaths annually.

Inclusion criteria

• above 18 years of age
• diagnosed with stable angina awaiting elective coronary angiography on dual antiplatelet therapy for at least 3 months with aspirin 81 mg per day maintenance dose and "brand name" clopidogrel 75 mg per day maintenance dose

Exclusion criteria

• generic clopidogrel, i.e. not "brand name,"
• recent acute coronary syndrome within 6 months
• active bleeding
• prior cerebrovascular event
• clinical instability after an index event
• use of an oral anticoagulation agent (coumadin derivative or other anticoagulant therapy (such as dabigatran, rivaroxaban or apixaban)
• platelet count < 100 x 106/µL
• hemoglobin < 10 g/dL
• serum creatinine > 2.5 mg/dL