Clopidogrel !

An oral antiplatelet drug that blocks the platelet ADP receptor P2Y12 for the platelet's whole life. It must be activated by the liver enzyme CYP2C19.

Updated 2026-11-01

Class: Antiplatelet drugs
Receptor: P2Y12 ADP receptor on platelets
ATC code: B01AC04
WHO Model List of Essential Medicines

P2Y12 ADP receptor on plateletsClopidogrel

The figure shows the human P2Y12 receptor with AZD1283, an experimental P2Y12 blocker. There is no structure with clopidogrel's active metabolite, which binds the receptor covalently.

Target in 3D: P2Y12 ADP receptor on platelets. PDB structure 4NTJ (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

Clopidogrel is a prodrug of the thienopyridine family. Most of it is broken down by esterases into an inactive acid; a smaller part is oxidised in two steps by liver CYP enzymes, mainly CYP2C19, into an active thiol metabolite. That metabolite binds the P2Y12 receptor irreversibly, so ADP can no longer activate the platelet and switch on the glycoprotein IIb/IIIa receptor. The block lasts for the rest of the platelet's life.

The liver turns clopidogrel into its active metabolite, mainly via CYP2C19
The metabolite binds P2Y12 irreversibly
ADP can no longer activate the glycoprotein IIb/IIIa receptor
Platelets stay blocked for their whole life (7 to 10 days)

Pharmacokinetics

Absorption: Rapidly absorbed by mouth.
Metabolism: Mostly hydrolysed by esterases to an inactive acid; the active metabolite comes from CYP enzymes, principally CYP2C19.
Elimination: About half in the urine and about half in the faeces.
Half-life: About 6 hours for clopidogrel; about 30 minutes for the active metabolite.
Onset and duration: Platelet inhibition starts about 2 hours after a dose; without a loading dose, the full effect takes several days.

Indications

Acute coronary syndrome, with or without ST elevation, usually together with aspirin. Myocardial Infarction (Heart Attack) →
Recent ischaemic stroke, to reduce new heart attacks and strokes. Ischaemic stroke →
Established peripheral arterial disease. Peripheral artery disease →

Adverse effects

Common

Bleeding, the most common adverse reaction
Nosebleeds and bruising
Headache, dizziness, nausea or stomach pain

Contraindications

Active pathological bleeding, such as a peptic ulcer or intracranial haemorrhage
Hypersensitivity to clopidogrel

Key interactions

Omeprazole or esomeprazole (CYP2C19 inhibitors): Reduce the active metabolite and the antiplatelet effect; combined use is avoided.
Opioids such as morphine: Delay and reduce its absorption by slowing the stomach; in acute coronary syndrome a parenteral antiplatelet may be considered.
Warfarin, NSAIDs, SSRIs, SNRIs and other antiplatelets: Increase the risk of bleeding.
Repaglinide (a CYP2C8 substrate): Its levels rise.

What is monitored

Signs of bleeding
CYP2C19 genotype, when available, identifies poor metabolisers who may need another P2Y12 blocker
Platelet count and blood smear if TTP is suspected

Administration and safety

Oral, with or without food
Not stopped early without the cardiology team, especially after a stent
Before planned surgery with high bleeding risk it is usually stopped several days ahead, according to the surgical plan
Platelet transfusion can help in bleeding because the active metabolite is short-lived

Nursing care

Check for active bleeding and ask which stomach medicines the patient takes (omeprazole, esomeprazole)
Watch for black stools, vomiting blood, blood in urine and unusual bruising
Report fever, weakness, confusion, purple spots or yellow skin: possible TTP
Teach the patient to tell every dentist and surgeon and not to stop it without advice

Pregnancy and breastfeeding

Published reports have not linked it to birth defects; a heart attack or stroke in pregnancy is an emergency and treatment is not withheld, but bleeding at delivery is a risk.

Test yourself

Think of the answer, then tap the question to see it.

Which enzyme activates clopidogrel, and what happens in poor metabolisers?

Mainly CYP2C19. People with two loss-of-function alleles make less active metabolite and get less platelet inhibition; another P2Y12 blocker may be considered.

Which proton pump inhibitors are avoided with clopidogrel, and why?

Omeprazole and esomeprazole, because they inhibit CYP2C19 and reduce the active metabolite.

How long does clopidogrel's effect on a platelet last?

For the platelet's whole life, 7 to 10 days, because the active metabolite binds P2Y12 irreversibly.

Which rare blood disorder has been reported with clopidogrel?

Thrombotic thrombocytopenic purpura (TTP): low platelets, haemolytic anaemia, neurological signs, kidney problems and fever.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: DailyMed - CLOPIDOGREL BISULFATE tablet (DailyMed (U.S. National Library of Medicine), 2026); Clopidogrel: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); eEML - Electronic Essential Medicines List (World Health Organization, 2025); 4NTJ: Structure of the human P2Y12 receptor in complex with an antithrombotic drug (RCSB Protein Data Bank, 2014).

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Representative model, for educational purposes only.