clopidogrel

Clopidogrel is an antiplatelet drug that works on a different switch than aspirin. If aspirin silences one alarm that calls platelets together, clopidogrel jams a separate one — a receptor on the platelet surface called P2Y12, which the signal molecule ADP uses to recruit more platelets into a growing plug.

It is a prodrug, meaning it is inactive when swallowed and must be converted by liver enzymes into its working form. People whose genes make those enzymes sluggish can get a weaker effect, which is one reason alternative P2Y12 inhibitors exist for higher-risk situations.

Its biggest role is after a coronary stent and after acute coronary syndromes, where it is given together with aspirin as dual antiplatelet therapy to keep the fresh stent from clotting while the artery lining heals over it. It is also used in some patients who cannot tolerate aspirin.

Like all antiplatelets, the cost is bleeding, and like aspirin its effect on platelets lasts for days after the last dose — an important fact when surgery is planned, since it is often paused in advance to let platelet function recover.