Which agent blocks the P2Y12 receptor to inhibit platelet aggregation after a transient ischaemic attack when aspirin is not suitable?

• A. Dipyridamole
• B. Clopidogrel
• C. Warfarin
• D. Aspirin

Answer: (B)

Blocking ADP-induced platelet activation via the P2Y12 receptor is a key way to prevent arterial thrombosis after a TIA when aspirin can’t be used. Clopidogrel is a prodrug that, once activated in the liver, irreversibly inhibits the P2Y12 receptor on platelets. By blocking this receptor, platelets can no longer respond to ADP, which reduces activation, aggregation, and thrombus formation. This mechanism specifically targets the ADP pathway, unlike aspirin which inhibits thromboxane A2 production, dipyridamole which works through increasing cyclic AMP via PDE inhibition and adenosine uptake, and warfarin which is an anticoagulant affecting clotting factor synthesis. Hence, clopidogrel is the agent that blocks the P2Y12 receptor to inhibit platelet aggregation after a TIA when aspirin isn’t suitable.