Ticagrelor differs from clopidogrel in reversibility and onset. Which pharmacological property of ticagrelor explains its faster offset and reversal compared to clopidogrel?

• A Ticagrelor is metabolized by CYP2C19 to active metabolite with shorter half-life than clopidogrel
• B Ticagrelor's renal clearance is faster than clopidogrel's hepatic clearance
• C Both drugs have similar offset kinetics — ticagrelor requires 5 days cessation before surgery like clopidogrel
• D Ticagrelor is a reversible direct-acting P2Y12 antagonist with a pharmacokinetic offset of ~3 days; clopidogrel's thienopyridine metabolite forms an irreversible covalent disulfide bond with P2Y12, lasting platelet lifetime ✓

Explanation

Clopidogrel is a prodrug requiring CYP2C19 activation to an active metabolite that forms an irreversible covalent bond (via disulfide linkage) with the P2Y12 receptor, blocking it permanently for the platelet's lifetime (7–10 days). Ticagrelor is a direct-acting, non-prodrug, reversible P2Y12 antagonist — it binds a different, allosteric site on P2Y12 non-covalently. When ticagrelor plasma levels fall (half-life ~7 hours, active metabolite ~9 hours), receptor function recovers. Platelet function normalizes in ~3 days after stopping ticagrelor, versus ~5 days for clopidogrel. Pre-surgery cessation: ticagrelor 3–5 days, clopidogrel 5–7 days.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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