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Platelet Function Testing in ACS — EECC MCQ

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HardCoronary Artery DiseasePlatelet Function Testing in ACSEECC

A 62-year-old man with ACS undergoes PCI. He is loaded with ticagrelor 180 mg in the emergency department. One hour later, platelet function testing shows high on-treatment platelet reactivity (HTPR). What does this finding imply?

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Correct answer: B — HTPR with ticagrelor is rare and should prompt assessment for drug absorption issues (e.g. vomiting, morphine-induced gastroparesis) rather than switching agents

Unlike clopidogrel (a prodrug requiring CYP2C19-mediated hepatic activation, where 30% of patients are poor metabolisers), ticagrelor is a direct-acting P2Y12 inhibitor that does not require metabolic activation. Therefore, CYP2C19 polymorphisms do not affect ticagrelor efficacy. HTPR with ticagrelor is uncommon and, when observed, is most often due to: (1) drug absorption issues — morphine (commonly given in ACS) delays gastric emptying and reduces ticagrelor absorption (IMPRESSION study); (2) vomiting the loading dose; (3) crush tablet if the patient cannot swallow. If morphine-induced gastroparesis is suspected, crushed ticagrelor or cangrelor (IV P2Y12 inhibitor) may be considered.

Reference: ESC (2023): Guidelines for the Management of Acute Coronary Syndromes