Antiplatelet therapy in cardiovascular disease

01Purpose and principlesWhat the treatment does and how it fits into care.

Aspirin irreversibly inhibits platelet cyclo-oxygenase; clopidogrel and prasugrel irreversibly inhibit P2Y12, while ticagrelor is reversible. Choice follows the vascular syndrome and revascularisation strategy.

Every prescription needs a documented indication, intended duration, bleeding review and plan for procedures. Combining an anticoagulant with one or two antiplatelets sharply increases bleeding risk.

Key points

Antiplatelets prevent platelet-rich arterial thrombosis; they are not interchangeable with anticoagulants.
Give aspirin as soon as possible in suspected ACS unless there is a true contraindication.
Dual antiplatelet therapy means aspirin plus one P2Y12 inhibitor; indication and duration depend on ACS, PCI and bleeding risk.
After MI, low-dose aspirin is generally continued indefinitely; clopidogrel is an alternative when aspirin is contraindicated.
Do not routinely prescribe aspirin for primary prevention of CVD.
Prasugrel is contraindicated after previous stroke or TIA and is generally unsuitable from age 75 unless a specialist judges benefit to exceed risk.
Never stop DAPT soon after coronary stenting without urgent advice from the treating interventional cardiology team unless life-threatening bleeding makes immediate action unavoidable.

02Indications, selection and cautionsWho may benefit, who needs urgent treatment and important alternatives.

ACS or stent thrombosisRed flag

New ischaemic chest pain, dynamic ECG change, troponin rise or abrupt symptoms after PCI require emergency ACS care.

Major bleedingRed flag

Haemodynamic compromise, melaena, haematemesis, intracranial symptoms or a large haemoglobin fall are high-risk features.

Minor nuisance bleeding

Bruising or brief epistaxis is common but still warrants adherence and interaction review rather than automatic cessation.

True aspirin hypersensitivity

Clarify bronchospasm, urticaria or anaphylaxis versus dyspepsia, because the alternative strategy differs.

High gastrointestinal risk

Previous ulcer or GI bleed, older age, NSAIDs, corticosteroids, anticoagulation and heavy alcohol use increase harm.

03Assessment before treatmentTests and checks that guide safe selection.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
12-lead ECG and serial troponinFirst step
Why
Assess suspected ACS or stent thrombosis.
Interpretation and limitations
Do not wait for troponin before activating emergency STEMI care when diagnostic ST elevation is present.
02
Full blood count
Why
Detect anaemia or thrombocytopenia before treatment and during suspected bleeding.
Interpretation and limitations
Compare with baseline and assess the clinical rate and site of blood loss.
03
Renal and liver function
Why
Estimate bleeding risk, procedural fitness and medicine suitability.
Interpretation and limitations
Organ dysfunction increases haemorrhagic risk and may change the wider antithrombotic plan.
04
Medication and procedure reconciliation
Why
Confirm indication, stent date/type, intended DAPT duration and interacting drugs.
Interpretation and limitations
NSAIDs, anticoagulants, SSRIs and corticosteroids may materially increase bleeding risk.
05
Bleeding-site investigation
Why
Locate and treat clinically important haemorrhage.
Interpretation and limitations
Use urgent neuroimaging for focal neurology/head injury and endoscopic or interventional evaluation for significant GI bleeding.

04Treatment approachPreparation, options, escalation and aftercare.

01FirstSuspected acute coronary syndromeFirst stepIschaemic chest pain or equivalent with possible ACS.

1Perform immediate ABC assessment, 12-lead ECG and activate the national ACS/reperfusion pathway when indicated.
2Give aspirin 300 mg orally as soon as possible unless genuinely contraindicated.
3Select the P2Y12 inhibitor with the ACS and PCI strategy, age, stroke history, anticoagulation and bleeding risk in mind.
4Document the loading dose, maintenance regimen and planned duration before discharge.

02NextLong-term secondary preventionStable after MI, PCI, ischaemic stroke/TIA or symptomatic peripheral arterial disease.

1Confirm the qualifying vascular diagnosis and whether DAPT remains required.
2Continue the nationally recommended single agent after the finite DAPT course; aspirin is generally indefinite after MI.
3Address smoking, lipids, blood pressure, diabetes and rehabilitation rather than treating antiplatelets as complete prevention.
4Review bleeding, adherence and the continuing indication at medication reviews.

03EscalationBleeding or urgent procedureEscalationMajor bleeding, intracranial symptoms or surgery before the planned antiplatelet course is complete.

1Resuscitate, identify the bleeding site, send FBC/coagulation/renal testing and obtain urgent specialist haemostasis support.
2Balance immediate bleeding control against stent thrombosis risk using the exact PCI date and indication.
3For non-emergency procedures, coordinate interruption and restart with the proceduralist and interventional cardiologist.
4After haemostasis, restart necessary antithrombotic treatment at the earliest safe time through a documented specialist plan.

05Regimens, contraindications and interactionsTreatment details and the circumstances that modify them.

Foundation antiplatelet for ACS and established atherosclerotic disease when indicated.

Aspirin

ACS loading: 300 mg orally once; long-term secondary prevention: 75 mg orally once daily.

Active bleeding, true hypersensitivity and previous ulcer; assess GI protection. Enteric coating does not remove systemic bleeding risk.

P2Y12 inhibitor for DAPT and an alternative single agent in several secondary-prevention settings.

Clopidogrel

75 mg orally once daily. In non-ST-elevation ACS, use a 300 mg or 600 mg loading dose; a 600 mg load may be considered before PCI in adults under 75. STEMI and fibrinolysis regimens are timing- and age-specific.

Bleeding; CYP2C19 interactions. Avoid routine co-prescribing with omeprazole or esomeprazole when another suitable PPI is available. In STEMI, patients older than 75 treated medically with fibrinolysis start 75 mg without a load; a 600 mg PCI load at age 75 or older needs individual bleeding-risk assessment.

Potent P2Y12 inhibition in ACS according to the invasive strategy and bleeding risk.

Ticagrelor

180 mg orally once as a loading dose, then 90 mg twice daily for up to 12 months after ACS unless stopped earlier for a clinical reason; use with aspirin 75 to 150 mg daily.

Bleeding, dyspnoea, bradyarrhythmia, severe hepatic impairment and important CYP3A interactions.

P2Y12 inhibitor for ACS treated with PCI.

Prasugrel

60 mg orally once as a loading dose at PCI, then 10 mg once daily; use 5 mg once daily if body weight is below 60 kg and, only if chosen after specialist risk assessment, from age 75.

Contraindicated with previous stroke/TIA or active bleeding; generally not recommended from age 75; higher bleeding risk at low body weight.

06Complications, monitoring and follow-upAdverse effects, response and longer-term review.

At every review, confirm indication, PCI date, intended stop date and who owns the plan.
Ask about melaena, haematemesis, haematuria, persistent epistaxis, bruising and neurological symptoms.
Check FBC and renal/liver function when clinically indicated, especially after bleeding or with combined antithrombotic therapy.
Review NSAIDs, anticoagulants, SSRIs, corticosteroids, alcohol and gastroprotection.
After ACS, monitor adherence closely because premature discontinuation can precipitate stent thrombosis.

07Special situationsVariants, exceptions and circumstances that change the usual approach.

Arterial versus atrial clot

Antiplatelets reduce atherothrombosis but are not a substitute for anticoagulation to prevent AF-related embolic stroke.

DAPT has an end date

The second agent is usually time-limited; the discharge plan must state duration and exceptions.

Prasugrel history matters

A remote TIA still makes prasugrel contraindicated.

PPI selection matters

Omeprazole and esomeprazole can reduce clopidogrel activation; choose an appropriate alternative when gastroprotection is needed.

Primary prevention is not secondary prevention

The net balance supporting aspirin after MI does not justify routine aspirin before a first CVD event.

08Common pitfallsFrequent interpretation and management errors.

01
Using aspirin instead of an anticoagulant for AF stroke prevention.
02
Stopping DAPT after a recent stent without establishing the PCI indication and date.
03
Prescribing prasugrel to someone with previous stroke or TIA.
04
Continuing dual or triple antithrombotic therapy with no documented review date.
05
Calling dyspepsia an aspirin allergy without clarifying the reaction.