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Dosing of Clopidogrel (Plavix) Based on CYP2C19 Genotype and the Effect on Platelet Reactivity in Patients with Stable Cardiovascular Disease

 

 

Clopidogrel (Plavix) is an oral, thienopyridine class antiplatelet agent used to inhibit blood clots in coronary artery disease (CAD), peripheral vascular disease, and cerebrovascular disease. The drug works by irreversibly inhibiting a receptor called P2Y12, an adenosine diphosphate ADP chemoreceptor. Adverse effects include hemorrhage, severe neutropenia, and thrombotic thrombocytopenic purpura (TTP).

 

It has been reported that variants in the CYP2C19 gene influence the pharmacologic and clinical response to the standard 75-mg daily maintenance dose. As a result, a study published in the Journal of the American Medical Association (2011;306:2221-2228) was performed. to test whether higher doses (up to 300 mg daily) improve the response to clopidogrel in the setting of loss-of-function CYP2C19 genotypes.

 

The study, ELEVATE-TIMI 56, was a multicenter, randomized, double-blind trial that enrolled and genotyped 333 patients with cardiovascular disease across 32 sites from October 2010 until September 2011. Study participants received maintenance doses of clopidogrel for 4 treatment periods, each lasting approximately 14 days, based on genotype. In total, 247 noncarriers of a CYP2C19*2 loss-of-function allele were to receive 75 and 150 mg daily of clopidogrel (2 periods each), whereas 86 carriers (80 heterozygotes, 6 homozygotes) were to receive 75, 150, 225, and 300 mg daily. The main outcome measures were platelet function test results (vasodilator-stimulated phosphoprotein [VASP] phosphorylation and VerifyNow P2Y12 assays) and adverse events.

 

Results showed that:

 

1. Treatment with 75 mg daily, CYP2C19*2 heterozygotes had significantly higher on-treatment platelet reactivity than did noncarriers (VASP platelet reactivity index [PRI]: mean, 70.0% vs. 57.5%, and VerifyNow P2Y12 reaction units [PRU]: mean, 225.6 vs. 163.6; P < .001 for both comparisons).

 

2. Among CYP2C19*2 heterozygotes, doses up to 300 mg daily significantly reduced platelet reactivity, with VASP PRI decreasing to 48.9% and PRU to 127.5 (P < .001 for trend across doses for both).

 

3. Whereas 52% of CYP2C19*2 heterozygotes were nonresponders (≥230 PRU) with 75 mg of clopidogrel, only 10% were nonresponders with 225 or 300 mg (P < .001 for both).

 

4. Clopidogrel, 225 mg daily, reduced platelet reactivity in CYP2C19*2 heterozygotes to levels achieved with standard clopidogrel, 75 mg, in noncarriers

 

5. In CYP2C19*2 homozygotes, even with 300 mg daily of clopidogrel, the mean VASP PRI was 68.3% and mean PRU, 287.0.

 

According to the authors, among patients with stable cardiovascular disease, tripling the maintenance dose of clopidogrel to 225 mg daily in CYP2C19*2 heterozygotes achieved levels of platelet reactivity similar to that seen with the standard 75-mg dose in noncarriers; in contrast, for CYP2C19*2 homozygotes, doses as high as 300 mg daily did not result in comparable degrees of platelet inhibition.

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