Ticagrelor is preferred over clopidogrel in STEMI for which pharmacokinetic/pharmacodynamic reason?
- A Ticagrelor directly and reversibly blocks P2Y12 receptors without requiring hepatic bioactivation, providing faster, more consistent platelet inhibition independent of CYP2C19 genotype ✓
- B Ticagrelor is a prodrug requiring CYP2C19 activation; since CYP2C19 poor metabolisers respond better, it is universally preferred
- C Ticagrelor inhibits COX-1 in addition to P2Y12 blockade, providing dual antiplatelet action
- D Ticagrelor is once-daily dosed due to its longer half-life compared to clopidogrel
Explanation
Clopidogrel is a prodrug that requires two-step hepatic activation by CYP2C19; loss-of-function CYP2C19 alleles (common in South Asians and Asians ~30%) result in reduced active metabolite formation and inadequate platelet inhibition. Ticagrelor is a direct, reversibly binding P2Y12 antagonist (a cyclopentyl-triazolo-pyrimidine) that does not require hepatic bioactivation, offering faster onset, greater and more consistent platelet inhibition regardless of CYP2C19 genotype. Unlike clopidogrel (once daily), ticagrelor requires twice-daily dosing. Ticagrelor does not inhibit COX-1.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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