Which of the following is an ADP receptor blocker that inhibits platelet aggregation?

• A. Abciximab
• B. Warfarin
• C. Clopidogrel
• D. Heparin

Answer: (C)

Blocking the ADP receptor on platelets prevents ADP from amplifying platelet activation and aggregation. Clopidogrel is a thienopyridine that, after hepatic activation, irreversibly blocks the P2Y12 receptor on platelets. By inhibiting this receptor, ADP cannot promote the conformational change and granule release that lead to fibrinogen binding via GPIIb/IIIa, so platelet aggregation is reduced. Abciximab works differently: it blocks the GPIIb/IIIa receptor directly, stopping the final common step of aggregation regardless of ADP signaling. Warfarin and heparin are anticoagulants acting on the coagulation cascade to prevent clot formation, not by inhibiting the platelet ADP receptor.