Which of the following is NOT an example of an irreversible P2Y12 antagonist?

Ticagrelor is indeed classified as a reversible P2Y12 antagonist, making it the correct response to the question about which option is not an example of an irreversible antagonist. Unlike irreversible agents, which permanently bind to the P2Y12 receptor and inhibit platelet activation for the lifespan of the platelet, ticagrelor binds reversibly. This reversible binding allows for a more controllable anticoagulation effect, meaning that its antiplatelet activity can diminish more quickly after discontinuation, compared to irreversible agents.

In contrast, ticlopidine, clopidogrel, and prasugrel are all irreversible P2Y12 antagonists. They exert their effects by creating a permanent bond with the receptor, which results in prolonged inhibition of platelet aggregation. This fundamental difference in their binding properties is crucial for understanding their respective uses, onset of action, duration, and management of bleeding risks in clinical scenarios.