Clopidogrel and ticlopidine inhibit platelet aggregation by selectively inhibiting the binding of adenosine diphosphate (ADP) to its platelet receptor, and irreversibly modifying the receptor. Consequently, platelets exposed to these drugs are affected for the remainder of their lifespan. Clopidogrel can be used for certain indications as an alternative to aspirin in patients who are intolerant of aspirin. It may also be used in combination with aspirin in patients who have had a cardiovascular event while on aspirin, and for acute management of ST elevation myocardial infarction and high-risk non–ST elevation acute coronary syndrome. Note that the use of clopidogrel may delay coronary surgery by up to 5 days—see adverse effects, below. The combination of aspirin and clopidogrel is also used to prevent thromboembolism after insertion of a coronary stent. The risk of myelotoxicity appears to be low and, unlike ticlopidine, no specific haematological monitoring is recommended. Ticlopidine can be used as an alternative drug in patients allergic to clopidogrel.

Adverse effects: Similar to other antiplatelet drugs, clopidogrel and ticlopidine prolong bleeding time and should be used with caution in patients at risk of increased bleeding. Clopidogrel has a similar adverse effect profile to aspirin (although in clinical trials gastrointestinal haemorrhage occurred less frequently with clopidogrel). Ticlopidine has more significant adverse reactions than clopidogrel, including agranulocytosis and neutropenia. Specific haematological monitoring is required if a patient is commenced on ticlopidine, at baseline and at regular intervals thereafter.