Clopidogrel: P2Y12 ADP Receptor Antagonist (Antiplatelet)
Clopidogrel (Plavix) is a thienopyridine prodrug that irreversibly inhibits the P2Y12 ADP receptor on platelets, preventing platelet aggregation. It is a cornerstone antiplatelet therapy for acute coronary syndromes (ACS) and percutaneous coronary interventions (PCI).
Clopidogrel requires hepatic bioactivation via CYP2C19. Patients who are CYP2C19 poor metabolisers (approximately 2–14% depending on ethnicity) have reduced efficacy and higher cardiovascular event rates. Genetic testing is recommended before use in high-risk patients.
Mechanism of Action
The active metabolite of clopidogrel irreversibly binds to the P2Y12 receptor on platelets, preventing ADP-induced platelet activation and aggregation. Since the inhibition is irreversible, platelet function recovers only as new platelets are produced (7–10 days after stopping).
Indications & Use
Acute coronary syndromes (NSTEMI, STEMI — dual antiplatelet with aspirin), post-PCI stent therapy (drug-eluting stent: typically 6–12 months DAPT), ischaemic stroke/TIA prevention, and peripheral arterial disease.
Dosage
Loading dose: 300 mg (or 600 mg for rapid onset in ACS). Maintenance: 75 mg once daily. No dose adjustment for renal impairment. Reduce dose in severe hepatic impairment.
Side Effects
Bleeding (most common — GI, surgical, intracranial). Bruising, dyspepsia. Rare: thrombotic thrombocytopenic purpura (TTP), aplastic anaemia. Risk of perioperative bleeding (stop 5–7 days before elective surgery).
Drug Interactions
Proton pump inhibitors (especially omeprazole): reduced clopidogrel efficacy via CYP2C19 inhibition — use pantoprazole instead if needed. NSAIDs/aspirin: increased bleeding risk. Warfarin: triple therapy markedly increases bleeding.
Contraindications
Active pathological bleeding (peptic ulcer, intracranial haemorrhage), hypersensitivity. Caution in severe hepatic impairment (reduced activation) and CYP2C19 poor metabolisers (consider alternative P2Y12 inhibitor).
Frequently Asked Questions
Why does clopidogrel interact with omeprazole?
Both clopidogrel and omeprazole are metabolised by CYP2C19. Omeprazole competitively inhibits this enzyme, reducing the conversion of clopidogrel to its active form and decreasing its antiplatelet effect. Pantoprazole has a less significant interaction.
How long before surgery should clopidogrel be stopped?
For elective surgery with bleeding risk, clopidogrel should be stopped 5–7 days before the procedure to allow platelet function to recover. For PCI stents, stopping antiplatelet therapy early increases stent thrombosis risk — always consult the prescribing physician.
Is there a genetic test to check if clopidogrel will work for me?
Yes — CYP2C19 genotyping identifies poor metabolisers (about 2–14% of the population). Poor metabolisers have reduced clopidogrel efficacy. Alternatives include prasugrel or ticagrelor, which do not require CYP2C19 activation.
References
- CURE Trial (clopidogrel in ACS)
- ESC NSTEMI Guidelines 2020
- EMA product information Plavix
Medical Disclaimer: This information is for educational purposes only and does not replace professional medical advice.