Antiplatelet drugs

Antiplatelet drugs are designed to decrease platelet aggregation to inhibit thrombus formation in the arterial circulation. Used to treat patients with cardiac and cerebrovascular conditions.

They are classified according to their mechanism of action:

• Irreversible cyclooxygenase inhibitors- aspirin, used for primary prevention of (cardio)vascular disease in older at risk patients, acute indications and secondary prevention
• Adenosine diphosphate (ADP) receptor inhibitors- clopidogrel, used for acute indications and secondary prevention; prasugrel (plus aspirin), used for the prevention of atherothrombotic events in patients with acute coronary syndrome undergoing percutaneous coronary intervention (PCI); ticagrelor (plus aspirin), used for the prevention of atherothrombotic events in patients with acute coronary syndrome; cangrelor (plus aspirin), is to be used under expert supervision only, in patients undergoing PCI who have not previously received clopidogrel, prasugrel or ticagrelor and for whom these drugs are not suitable.
• Phosphodiesterase inhibitors- cilostazol is indicated for the improvement of the maximal and pain-free walking distances in patients with intermittent claudication. Dose reduction is advised in patients receiving medicines which inhibit CYP3A4 and CYP2C19. Cilostazol is contraindicated in patients with moderate or severe hepatic impairment, and those with creatinine clearance of ≤ 25 ml/min.
• Protease-activated receptor 1 (PAR1) antagonists- vorapaxar is not approved in the UK, but is used elsewhere to reduce the risk of thrombotic cardiovascular events in patients with a history of myocardial infarction (MI) or with peripheral arterial disease (PAD). Contraindicated in patients with a history of stroke, transient ischemic attack (TIA), or intracranial hemorrhage (ICH), or with active bleeding. Metabolism is mainly hepatic, so use is not recommended in patients with severe liver impairment.
• Glycoprotein IIB/IIIA inhibitors block the binding of fibrinogen to receptors on platelets- abciximab, used as an adjunct to unfractionated heparin and aspirin for the prevention of ischaemic complications in high-risk patients undergoing percutaneous transluminal coronary intervention, as a once only treatment; eptifibatide (plus unfractionated heparin and aspirin) and tirofiban (plus unfractionated heparin, aspirin, and clopidogrel) are used to prevent early myocardial infarction in patients with unstable angina or non-ST-segment-elevation myocardial infarction, and the tirofiban combination therapy can be used in non-ST-segment-elevation myocardial infarction patients undergoing PCI.
• Adenosine reuptake inhibitors- dipyridamole, used as an adjunct to oral anticoagulation for prophylaxis of thromboembolism associated with prosthetic heart valves and for secondary prevention of ischaemic stroke and transient ischaemic attacks.
• Thromboxane receptor antagonists- none are approved but see Davı et al. (2012) for rationale behind their development
• Thromboxane synthase inhibitors- none are approved but see Davı et al. (2012) for rationale behind their development