Antiplatelet Medications

Arterial versus venous clots

Clot composition depends on flow. In arteries, blood races past an area of vessel injury — often a ruptured atherosclerotic plaque — and platelets stick first, forming a dense "white thrombus." Because platelet activation drives arterial clotting, antiplatelets are the mainstay of arterial disease. In veins, blood pools and stagnates, letting the coagulation cascade build a loose, fibrin-rich "red thrombus" with relatively fewer platelets, which is why anticoagulants dominate venous disease. This is why atrial fibrillation and deep vein thrombosis call for an anticoagulant, while coronary artery disease and prior ischemic stroke call for an antiplatelet.

Aspirin

Aspirin irreversibly acetylates cyclooxygenase-1 (COX-1) inside the platelet, permanently blocking synthesis of thromboxane A2, a potent promoter of platelet aggregation and vasoconstriction. Because platelets are anucleate and cannot make new enzyme, this effect lasts the entire lifespan of that platelet — roughly a week to ten days — until the marrow replaces it, so aspirin's effect outlasts the drug itself in the bloodstream.

P2Y12 receptor inhibitors

These drugs block the ADP receptor (P2Y12), preventing a second, amplifying pathway of platelet activation. Clopidogrel is an oral prodrug requiring hepatic activation by CYP2C19; genetically poor metabolizers generate less active drug and less protection, and drugs that inhibit CYP2C19 — notably omeprazole — can blunt clopidogrel's effect the same way. Prasugrel is also a prodrug but converts more efficiently, giving greater and more consistent potency; that same potency raises bleeding risk, and prasugrel is contraindicated after a prior stroke or transient ischemic attack because of unacceptable intracranial bleeding risk. Ticagrelor binds P2Y12 reversibly rather than permanently and carries a distinctive side effect of dyspnea, thought to relate to adenosine signaling rather than cardiopulmonary disease. Cangrelor is an intravenous P2Y12 inhibitor with a very short half-life, used for rapid, reversible platelet inhibition during procedures such as catheterization when an oral agent hasn't had time to act.

Glycoprotein IIb/IIIa inhibitors

Abciximab, eptifibatide, and tirofiban block the glycoprotein IIb/IIIa receptor, the final common pathway through which fibrinogen cross-links platelets. Because they shut down aggregation at this last step, they are extremely potent and reserved for periprocedural use — typically intravenous, around percutaneous coronary intervention — rather than long-term outpatient therapy, given bleeding risk and the need for close monitoring.

Dipyridamole, cilostazol, and vorapaxar

Dipyridamole raises intracellular cyclic AMP in platelets, reducing reactivity, and is sometimes paired with aspirin for stroke prevention. Cilostazol works through a related phosphodiesterase-inhibiting mechanism with a distinct niche: it improves walking distance in peripheral arterial disease with claudication, leg pain from inadequate blood flow during exertion. Because phosphodiesterase III inhibitors have been linked to increased mortality in heart failure, cilostazol is contraindicated in heart failure of any severity. Vorapaxar inhibits the PAR-1 thrombin receptor on platelets and is used for secondary prevention in select patients with established atherosclerotic disease, though its bleeding risk, including intracranial hemorrhage, limits its use.

Indications and clinical management

Antiplatelet therapy is central to secondary prevention after myocardial infarction and ischemic stroke, reducing recurrent events. After coronary stent placement, patients typically receive dual antiplatelet therapy — aspirin plus a P2Y12 inhibitor — because the newly placed stent is a foreign surface prone to platelet-driven clotting until it endothelializes. How long dual therapy continues is a risk-balanced decision weighed against bleeding risk, stent type, and clinical presentation, not a fixed rule. In peripheral arterial disease, antiplatelets, and cilostazol specifically for claudication, reduce ischemic events and improve symptoms.

Bleeding is the dominant adverse effect across every antiplatelet class, ranging from bruising and gastrointestinal bleeding to, rarely, intracranial hemorrhage. Before elective surgery, clinicians weigh holding an antiplatelet against the risk of a thrombotic event, especially with a recent stent, since stopping too early can trigger clotting on the stent itself; this decision is individualized with the prescribing specialist. The highest-risk scenario is triple therapy — dual antiplatelet therapy plus an anticoagulant, as in a patient with both a stent and atrial fibrillation — which compounds bleeding risk substantially and is minimized in duration and agent count whenever possible.