• Aspirin
• Clopidogrel
• Dipyridamole
• Prasugrel

• Primary and secondary prevention of atherosclerotic disease
• Management of acute coronary syndromes (NSTEMI & STEMI)
• Suspected/Actual TIA
• Acute ischaemic Stroke

• Secondary prevention of atherosclerotic disease and embolic events where aspirin is contraindicated
• Management of neurovascular events when aspirin is not tolerated
• Management of acute coronary syndromes (NSTEMI & STEMI)
• Prevention of atherothrombotic events in percutaneous coronary intervention
• The Royal College of Stroke Physicians currently recommends clopidogrel as the first line treatment for the long-term prevention of vascular events for patients following ischaemic stroke or TIA

• Secondary prevention of ischaemic stroke and transient ischaemic attack
• Adjunct to oral anticoagulation for prophylaxis of thromboembolism associated with prosthetic heart valves

• Prevention of atherothrombotic events in patients with acute coronary syndrome (adjunct with aspirin)
• Alternative to clopidoigrel in patients undergoing PCI

• Prevention of atherothrombotic events in patients with acute coronary syndrome (adjunct with aspirin)
• Alternative to clopidogrel in patients undergoing PCI

• All drugs:
  • Active bleeding
• Aspirin only:
  • Hypersensitivity to aspirin or NSAIDs
  • Children <16 years old (risk of Reye's syndrome)
  • Bleeding disorders e.g. Haemophilia
  • Pregnancy
• Ticagrelor
  • History of intracranial haemorrhage
• Prasugrel
  • History of stroke or TIA

• Aspirin and/or Clopidogrel:
  • Patients at high risk of bleeding
  • Active/previous peptic ulceration
  • Uncontrolled severe (malignant) hypertension, ensure BP is well controlled before starting treatment
  • Renal insufficiency
  • Hepatic insufficiency
  • Pregnancy/breastfeeding
• Aspirin only:
  • Asthma
  • G6DP deficiency
• Dipyridamole only:
  • Unstable angina or recent myocardial infarction
  • Left ventricular outflow obstruction
  • Heart failure
  • Migraine
  • Myasthenia gravis
• Ticagrelor only:
  • Asthma
  • COPD
• Prasugrel only:
  • Patients at risk of bleeding
  • Body weight less than 60kg

Aspirin, clopidogrel, ticagrelor, prasugrel and dipyridamole are anti-platelet agents. These agents decrease platelet aggregation and inhibit thrombus formation in the arterial circulation. Anti-platelet drugs are active in aiding resolution of 'white clots' which are mainly composed of platelets with little fibrin.

Aspirin is an irreversible inhibitor of the enzyme cyclo-oxygenase. This prevents the formation of thromboxanes which stimulate platelet aggregation. Inhibition of cyclo-oxygenase also prevents formation of prostaglandins, which are involved in the sensitisation of peripheral pain receptors to noxious stimuli. This property explains the use of aspirin as an anti-inflammatory and analgesic agent.

Clopidogrel is an Adenosine Diphosphate (ADP) receptor antagonist and blocks ADP from binding to platelet receptors. This inhibits activation of the GP IIb/IIIa complex and prevents platelet activation.

The mechanism of action of Dipyridamole is not yet fully understood, however it is thought to exhibit its action as an anti-platelet agent by inhibiting phosphodiesterase-mediated breakdown of cyclic AMP. This inhibits platelet activation via various mechanisms.

Anti-platelet effects of Aspirin and Clopidogrel (or Aspirin and Dipyridamole) in combination are synergistic.

• Haemorrhage at any site: e.g. gastrointestinal, intracranial
• Although there is a suggestion that Clopidogrel causes less haemorrhage than Aspirin, differences are small and the use of any anti-platelet agent carries a risk of bleeding
• Hypersensitivity

• Aspirin causes gastric erosions, due to its effect on prostaglandins (PGE2 and PGI2 which stimulate mucus and bicarbonate secretion and cause vasodilation, thereby protecting gastric mucosa)
• Bronchospasm (again through a prostaglandin effect), associated with chronic rhinosinusitis and nasal polyps
• Tinnitus

• Gastrointestinal upset (e.g. nausea, diarrhoea, abdominal pains)
• Dizziness, vertigo
• Paraesthesia
• Hepatic and biliary damage

• Gastrointestinal upset
• Vasodilatation resulting in dizziness, headache, hot flushes, hypotension and tachycardia
• Worsening of ischaemic heart disease symptoms
• Haemorrhage is less common than with other anti-platelet agents

• Bruising
• Dyspnoea

• Rash
• Angioedema

• Aspirin and Serotonin Selective Reuptake Inhibitors are associated with an increased risk of bleeding
• Some NSAIDS (e.g. Ibuprofen) inhibit the anti-platelet action of aspirin
• Aspirin reduces the excretion of Methotrexate, which may increase the risk of Methotrexate toxicity
• Prescribed alongside acetazolamide can lead to toxicity

• Concurrent Proton Pump Inhibitors may reduce the anti-platelet action of Clopidogrel

• Anti-epileptics (e.g. carbmazepine, phenobarbital and phenytoin) interact with ticagrelor to reduce its antiplatelet effect.
• Clarithromycin, simvastatin and azole antifungals interact with ticagrelor to increase its antiplatelet effect (and therefore increase the risk of bleeds occurring)