2.9 Antiplatelet drugs
Aspirin (dispersible tablets) should be used after myocardial infarction, in unstable and stable angina, for primary prevention in high-risk individuals, in patients with a strong family history of bowel cancer, in "low-risk" patients in atrial fibrillation and in thrombotic cerebrovascular disease. There is no conclusive evidence that enteric-coated preparations in general are better tolerated. In acute myocardial infarction, a loading dose of 300mg of dispersible or crushed (if enteric-coated) aspirin is given as early as possible after the onset of symptoms, followed by a daily maintenance dose of 150mg daily for at least one month. Thereafter, a daily maintenance dose of 75 - 150mg dispersible is suggested.
Abciximab (IV injection) is a monoclonal antibody, which inhibits platelet aggregation and thrombus formation. It is used by specialists as an adjunct to heparin and aspirin for the prevention of ischaemic complications in high-risk patients undergoing percutaneous transluminal coronary angioplasty (PTCA).
Dipyridamole (m/r capsules) in the modified-release formulation is used for the prevention of occlusive vascular events as per NICE TA210. An injectable form is used for certain diagnostic purposes such as myocardial perfusion imaging.
Clopidogrel (75mg tablets) is a prodrug. One of its metabolites inhibits platelet aggregation by irreversibly and selectively blocking adenosine diphosphate (ADP) at its platelet receptor. It is used in the treatment of ischaemic heart disease. Its use is restricted to patients who are truly intolerant to aspirin. It is contra-indicated in patients at high risk of GI bleeds. It can also be used in combination with aspirin in stented angioplasty, administered for 2 days before and for 4 weeks after the procedure. It is used in combination with aspirin for up to one year for unstable angina or acute coronary syndrome and four weeks in patients with ST segment elevation acute myocardial infarction.
It is also used for the prevention of occlusive vascular events as per NICE TA210.
Prasugrel (10mg tablets, Efient) is a pro-drug which inhibits platelet activation and aggregation throught the irreversible binding of its active metabolite to ADP receptors on platelets. It is available for restricted use co-administered with aspirin for the prevention of atherothrombotic events in patients with acute coronary syndrome undergoing primary or delayed percutaneous coronary intervention. Use is restricted to patients who are eligible to receive the 10mg dose of prasugrel - 18-75 years old, and >60kg. Treatment is initiated with a single 60 mg loading dose then continued at 10 mg once daily [SMC 562/09].
Ticagrelor (90mg film-coated tablets, Brilique®) is an oral antagonist at the P2Y12 adenosine diphosphate receptor, which inhibits platelet aggregation and thrombus formation. It available for restricted use co-administered with aspirin, for the prevention of atherothrombotic events in adult patients with acute coronary syndromes (unstable angina, non ST elevation myocardial infarction [NSTEMI] or ST elevation myocardial infarction [STEMI]); including patients managed medically, and those who are managed with percutaneous coronary intervention (PCI) or coronary artery by-pass grafting (CABG) [SMC 699/11].
Tirofiban (IV infusion) inhibits platelet aggregation by binding to platelet glycoprotein IIb/IIIa receptors. It is used by consultant cardiologists in combination with heparin and aspirin to prevent early myocardial infarction in patients with unstable angina or non-Q-wave myocardial infarction.
Restricted to use in CCU and the cath labs
Clopidogrel 300mg tablet is restricted to use in the CCU and cath labs. It is used to reduce pill burden for loading doses in patients suffering from acute coronary syndrome, pre-treatment before PCI [including 600mg loading dose off-label use].
PRESCRIBING POINTS FOR ANTIPLATELET DRUGS
- Antiplatelet drugs inhibit thrombus formation in arterial blood vessels. They have little effect on formed thrombi.
- Aspirin reduces mortality following myocardial infarction and the risk of progression to myocardial infarction in patients with ischaemic heart disease. It is also an effective primary preventative therapy, and is recommended when the 10-year coronary risk exceeds 15%.
- Dispersible aspirin should be given with or after food.
- Aspirin, clopidogrel and ticagrelor are contra-indicated in patients with active pathological bleeding and bleeding disorders.