Clopidogrel Pharmacogenetic Score System

There is a large inter-individual variability of biological antiplatelet responsiveness in patients treated with clopidogrel. Our previous study suggested that in clopidogrel treated Chinese patients with acute coronary syndromes(ACS),carriers of at least one CYP2C19 loss-of-function allele could predict greater risk of high on-treatment platelet reactivity (HPR), with the impact mainly attributing to CYP2C19*2. But as we know, CYP2C19*2 could only explain a small proportion of the variability. Various clinical and demographic variables have been considered to influence response to antiplatelet therapy.

Study objectives:

The present study aims to evaluate candidate variables,including CYP2C19 gene polymorphisms, clinical and demographic variables,to establish a simple risk score to identify patients who are at risk for HPR and composite cardiovascular outcomes .

Study design:

Step 1: Population enrollment and medication This mono-center study will be conducted in General Hospital of Chinese People's Liberation Army. Consecutive patients more than 18 years old admitted for ACS will be recruited after giving informed consents. After admission, all enrolled patients will be treated with 100 mg aspirin and 75mg clopidogrel per day. A loading dose of 300 mg clopidogrel will be given to patients undergoing coronary angiography.

Step 2: Clinical and demographic data collection A detailed demographic and medical data will be extracted from medical charts and prescription records. For the development of the risk score system, we will chose variables that are available in routine clinical practice. Clinical candidate variables include smoking history, diabetes,hypertension, renal failure with a serum creatinine>1.5mg/dL-1, hypercholesterolemia, left ventricular dysfunction, age, gender, acute coronary syndrome on admission and co-medication with statins, calcium channel inhibitor, and proton pump inhibitors.

Step 3 : Platelet function measurements and Genotyping After 5 days maintenance dose of clopidogrel administration, blood samples will be drawn for light transmittance aggregometry (LTA) testing, using an APACT-4 aggregometer (LABiTec, Germany). The magnitude of on-treatment platelet reactivity was quantified using LTA with 20µmol/L ADP(adenosine disphosphate) as the agonist. Aggregation was expressed as the maximal percentage change in light transmittance from baseline, with platelet-poor plasma as the reference.

Genomic DNA will be extracted from the peripheral blood leucocytes of each patient. The loss of function alleles, CYP2C19*2 (rs4244285) and CYP2C19*3 (rs4986893), will be genotyped by the polymerase chain reaction(PCR)-ligase detection reactions(LDR)sequencing method.

Step 4: Follow-up At one year, the incidence of composite cardiovascular outcomes will be assessed by review of the patients'charts on re-admission or by telephone interview. Telephone interviewers are blinded with respect to the results of platelet aggregation and genotypes.

Step 5: Statistical analysis and development of risk score Logistic regression and Cox proportional hazards survival regression will be used to develop the risk score system with the candidate variables including clinical and demographic variables, CYP2C19 genotypes, and platelet aggregation.