Pharmacogenetic Approach to Anti-platelet Therapy for the Treatment of ST-segment Elevation Myocardial Infarction (STEMI)

Dual anti-platelet therapy following percutaneous coronary intervention (PCI) for the treatment of STEMI has traditionally consisted of aspirin and clopidogrel. Despite this treatment approach, a substantial portion of patients experience recurrent adverse cardiovascular events including death, myocardial infarction, and stent thrombosis. This persistent vulnerability has been associated with inadequate platelet inhibition in response to clopidogrel administration, a phenomenon referred to as high on-treatment platelet reactivity. Although multiple variables have been implicated in altered clopidogrel response, mounting evidence has suggested a crucial role for common genetic variants including: CYP2C19*2, *17, and ABCB1 3435 C>T alleles.

Presence of the CYP2C19*2 allele has been associated with a 1.5- to 6-fold increased risk of cardiovascular death, myocardial infarction, and stent thrombosis following PCI in patients treated with clopidogrel. These findings, recently bolstered by 2 separate meta-analyses, led the American Food and Drug Administration to issue a boxed warning for clopidogrel stating that poor metabolizers may not receive the full benefit of the drug. The ABCB1 3435 TT genotype has also been linked with increased adverse cardiovascular events in individuals treated with clopidogrel following PCI for an acute coronary syndrome. In contrast, the CYP2C19*17 gain-of-function allele appears to enhance the activity of clopidogrel and has been associated with reduced ischemic events but increased bleeding.

As a result of these findings, experts have begun to advocate for routine genotyping in the context of PCI. A personalized approach to dual anti-platelet therapy following PCI is feasible given the presence of treatment alternatives such as prasugrel that are capable of overcoming clopidogrel resistance. Selective administration of prasugrel to patients at increased risk of clopidogrel resistance has the potential to successfully minimize adverse ischemic events, while simultaneously minimizing associated bleeding events and health care costs. A prospective pharmacogenomic approach to anti-platelet therapy has been previously hampered by limited access and the time-delay associated with genetic testing. The development of point-of-care genetic testing for the CYP2C19*2, *17, and ABCB1 3435 C>T alleles that requires minimal training to perform carries the potential to overcome these obstacles and may facilitate the incorporation of pharmacogenetic strategies into routine clinical practice.

Patients receiving PCI in the context of STEMI will undergo point-of-care genetic testing for the CYP2C19*2, *17, and ABCB1 3435 C>T alleles. CYP2C19*2 carriers and individuals homozygous for the ABCB1 3435 T allele will subsequently be randomized to prasugrel 10mg daily for 1 month or clopidogrel 150mg daily for 1 week followed by 75mg daily. The remaining individuals without an at-risk genotype will receive standard therapy with clopidogrel. At the end of the 1 month period, efficacy of the treatment strategies will be evaluated using VerifyNow platelet function testing. The effect of the CYP2C19*17 allele will be prospectively evaluated during the treatment period.

Inclusion criteria

• Males and Females between the ages of 18 and 75 years
• STEMI patients treated with percutaneous coronary intervention
• Able to provide informed consent
• Able to comply with assigned treatment strategy and attend 1 month follow-up visit

Exclusion criteria

• Receiving anti-platelet therapy other than aspirin and clopidogrel
• Receiving anti-coagulation with warfarin or dabigatran
• History of stroke or transient ischemic attack
• Platelet count < 100 000/μL
• Known Bleeding Diathesis
• Hematocrit <30% or >52%
• Severe Liver Dysfunction
• Renal Insufficiency (Creatinine Clearance < 30ml/min)
• Pregnant females