Antiplatelet drugs (Antiaggregants) : Definition, Classification, List, Example, Mechanism of Action, Uses, Side Effects, Contraindications, & Interactions
Definition
- Antiplatelet drugs (Antithrombotic drugs) are drugs which interfere with platelet function and are useful in the prophylaxis of thromboembolic disorders.
Classification
COX inhibitor
Mechanism of action
- Aspirin acetylates and inhibits the enzyme COX1 and TX synthase-inactivating them irreversibly.
- Aspirin also inhibits COX1 and PGI2 synthesis in vessel wall. However, since intimal cells can synthesize fresh enzyme, activity returns rapidly.
- It is possible that at low doses (75-150 mg/day or 300 mg twice weekly), TXA2 formation by platelets is selectively suppressed, whereas higher doses (> 900 mg/ day) may decrease both TXA2 and PGI2 production.
E.g.
- Aspirin
P2Y12 receptor antagonist (Gi coupled P2Y Ac)
- P2Y 12 (Gi coupled P2Y Ac) type of purinergic receptors mediate adenylyl cyclase inhibition by ADP.
- As a result of P2Y12 receptor blockage, activation of platelets is interfered. It prevents fibrinogen binding to platelets without modifying GPIIb/IIIa receptor.
E.g.
- Clopidogrel
- Prasugrel
- Ticagrelor
- Ticlopidine
Phosphodiesterase inhibitors
E.g.
- Dipyridamole
- Cilostazol
Glycoprotein (GP) IIb/IIIa receptor antagonists
- GP IIb/IIIa antagonists are a new class of potent platelet aggregation inhibitors.
- The GP IIb/IIIa is an adhesive receptor (integrin) for fibrinogen and vWF through which agonists like collagen, thrombin, TXA2, ADP, etc. induce platelet aggregation.
Mechanism of action
- GP IIb/IIIa antagonists act by blocking the key receptor involved in platelet aggregation. Thus, GP IIb/IIIa antagonists block aggregation induced by all platelet agonists.
E.g.
- Abciximab
- Tirofiban
- Eptifibatide
Also Read: Drugs Affecting Coagulation, Bleeding & Thrombosis
Uses
For certain indications like maintenance of vascular recanalization, stent placement, vessel grafting, etc. potent inhibition of platelet function is required. This is achieved by combining antiplatelet drugs which act by different mechanisms.
- Coronary artery disease
- Cerebrovascular disease
- Coronary angioplasty, stents, bypass implants
- Prosthetic heart valves and arteriovenous shunts
- Venous thromboembolism
- Peripheral vascular disease
