Patients with the CYP2C19*2 poor metabolizer genotype have reduced clopidogrel response (clopidogrel resistance). The FDA now mandates genotype testing before initiation. Which statement best describes the clinical management implication?
- A CYP2C19*2 carriers can be managed with doubled clopidogrel loading doses to achieve adequate platelet inhibition
- B CYP2C19*2 carriers should receive prasugrel or ticagrelor (which do not require CYP2C19 activation) rather than clopidogrel for ACS/PCI, as demonstrated by the TRITON-TIMI 38 and PLATO trials ✓
- C Aspirin dose should be tripled in CYP2C19*2 carriers to compensate for inadequate clopidogrel efficacy
- D Vorapaxar (PAR-1 antagonist) should replace clopidogrel in CYP2C19*2 carriers as a thienopyridine-independent alternative
Explanation
Clopidogrel is a thienopyridine prodrug requiring hepatic bioactivation primarily by CYP2C19 (two-step oxidation to active thiol metabolite). The CYP2C19*2 allele (rs4244285, a splice-site loss-of-function variant) is the most common clopidogrel resistance allele, present in approximately 30% of South Asians and East Asians. *2 carriers produce significantly less active metabolite, resulting in inadequate P2Y12 receptor inhibition and higher rates of stent thrombosis and major adverse cardiac events (MACE). Prasugrel (requires only one CYP3A4/CYP2B6 step, largely bypassing CYP2C19) and ticagrelor (a non-thienopyridine, directly acting P2Y12 antagonist requiring no metabolic activation) are not affected by CYP2C19 genotype. Doubling clopidogrel dose in *2 carriers provides insufficient platelet inhibition and is not recommended per CPIC guidelines.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.