Antiplatelet Agents

📋 Key Information Summary

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Antiplatelet agents are cornerstone therapy for preventing arterial thrombosis in acute coronary syndromes (ACS), percutaneous coronary intervention (PCI), ischaemic stroke, and peripheral arterial disease (PAD).
Aspirin irreversibly acetylates cyclooxygenase-1 (COX-1)，reducing thromboxane A2 production. Standard dose is 100 mg (75–150 mg) daily for long-term secondary prevention.
Dual antiplatelet therapy (DAPT) with aspirin plus a P2Y12 inhibitor is standard post-ACS and post-PCI to mitigate stent thrombosis and recurrent ischaemic events.
P2Y12 inhibitors: Clopidogrel (prodrug, variable response), Ticagrelor (reversible, more potent, dyspnoea side-effect), and Prasugrel (contraindicated in prior stroke/TIA).
DAPT duration is individualised: typically 12 months post-ACS, but can be shortened (1–3 months) or extended based on ischaemic vs. bleeding risk (DAPT score).
GP IIb/IIIa inhibitors (abciximab, eptifibatide, tirofiban) are reserved for high-risk PCI or bail-out situations; administered IV in hospital settings.
Bleeding is the major risk. Gastroprotection with a PPI is recommended for patients with high GI bleeding risk on DAPT.
Perioperative management requires careful planning; generally stop ticagrelor 5 days, clopidogrel 5 days, and aspirin 7 days before elective surgery if indicated.
Pharmacogenomic testing for CYP2C19 loss-of-function alleles can guide clopidogrel use in high-risk settings (e.g., post-PCI).
Aspirin is not recommended for primary prevention of cardiovascular disease in the general population due to bleeding risk outweighing benefit.
Aboriginal and Torres Strait Islander peoples have higher CVD burden; ensure equitable access, health-literate education, and consideration of remote pharmacy supply.

Antiplatelet Agents clinical infographic — pathophysiology, clinical clues, diagnosis, imaging, and management — Tap or click image to enlarge — Antiplatelet Agents: pathophysiology, clinical clues, diagnosis, imaging, and management.

Introduction & Australian Epidemiology

Antiplatelet agents form a critical pillar in the management of atherothrombotic disease, targeting distinct pathways in platelet activation and aggregation to prevent arterial thrombosis. Their use is firmly established in the secondary prevention of cardiovascular，cerebrovascular，and peripheral arterial diseases.

In Australia, cardiovascular disease (CVD) remains a leading cause of mortality，accounting for approximately 25% of all deaths. Acute coronary syndromes (ACS) affect over 50,000 Australians annually. The burden is significantly higher among Aboriginal and Torres Strait Islander peoples，who experience CVD at younger ages and with greater severity. Antiplatelet therapy is integral to national guidelines from the Cardiac Society of Australia and New Zealand (CSANZ) and the National Heart Foundation (NHF).

Platelet Physiology & Activation

Platelets are anucleate cell fragments derived from megakaryocytes. Upon vascular injury，exposed collagen and von Willebrand factor (vWF) mediate platelet adhesion via glycoprotein (GP) Ib-IX-V and GP VI receptors. This triggers activation，leading to:

Release of agonists such as ADP and thromboxane A2 (TxA2)，which amplify activation via P2Y12 and TxA2 receptors.
Shape change and granule secretion.
Conformational activation of the GP IIb/IIIa receptor，which binds fibrinogen and mediates platelet cross-linking，forming the final common pathway of aggregation.

Antiplatelet drugs inhibit key steps in this cascade: TxA2 synthesis (aspirin)，ADP signalling (P2Y12 inhibitors)，and fibrinogen binding (GP IIb/IIIa inhibitors).

Aspirin (COX-1 Inhibition)

Aspirin irreversibly acetylates serine-530 of cyclooxygenase-1 (COX-1)，preventing the conversion of arachidonic acid to TxA2 for the platelet's lifespan (7–10 days). This effect reduces platelet aggregation in response to various stimuli.

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Aspirin

Cardiprin®, Aspro Clear® · NSAID, Antiplatelet

Adult dose Acute MI/ACS: 300 mg loading dose (oral or chewed). Secondary prevention: 100 mg (75–150 mg) once daily.

Paediatric dose Kawasaki disease: 3–5 mg/kg/day (low dose) after initial high-dose phase. Not for general paediatric antiplatelet use.

Route / Frequency Oral, once daily.

Renal adjustment Caution in eGFR <30 mL/min; avoid if possible due to bleeding risk. No dose adjustment for antiplatelet effect.

Hepatic adjustment Avoid in severe hepatic impairment (risk of coagulopathy).

PBS status ✔ PBS General Benefit

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Key Safety Point: Concurrent use with other NSAIDs (e.g., ibuprofen) may attenuate aspirin's antiplatelet effect. Use paracetamol for analgesia where possible. Gastroprotection with a PPI (e.g., omeprazole 20 mg daily) is recommended for patients with GI risk factors.

P2Y12 Inhibitors (Clopidogrel, Ticagrelor)

These agents block the P2Y12 ADP receptor on platelets，attenuating activation and amplification. Choice depends on clinical context (ACS vs. elective PCI)，ischaemic/bleeding risk，and patient factors.

Feature	Clopidogrel	Ticagrelor
Mechanism	Irreversible P2Y12 antagonist (prodrug)	Reversible, direct-acting P2Y12 antagonist
Onset	2–6 hours (300–600 mg load)	30 minutes (180 mg load)
ACS Dose	300–600 mg load, then 75 mg daily	180 mg load, then 90 mg BD
Key Limitation	Variable response due to CYP2C19 polymorphisms	Dyspnoea (≈14%)，ventricular pauses
Perioperative stop	5 days	5 days

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Clopidogrel

Plavix®, Iscover® · P2Y12 inhibitor

Adult dose ACS: 300–600 mg STAT, then 75 mg daily. Stroke/PAD: 75 mg daily.

Renal adjustment No dose adjustment, but use with caution in severe impairment.

PBS status ✔ PBS General Benefit

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Ticagrelor

Brilinta®, Possia® · P2Y12 inhibitor

Adult dose ACS: 180 mg STAT, then 90 mg twice daily (with aspirin ≤100 mg daily).

Renal adjustment No dose adjustment.

PBS status ⚠️ PBS Authority Required (for ACS)

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Note: Prasugrel (Effient®) is an alternative potent irreversible P2Y12 inhibitor. It is contraindicated in patients with prior stroke/TIA and generally avoided in patients ≥75 years or <60 kg. PBS Authority Required.

GP IIb/IIIa Inhibitors & Indications

Glycoprotein IIb/IIIa inhibitors are intravenous agents that block the final common pathway of platelet aggregation. They are used in acute，hospital-based settings for high-risk interventions.

Common Agent

Eptifibatide (Integrilin®)

Small molecule; reversible. Bolus + infusion.

Setting: Cath lab / CCU

Common Agent

Tirofiban (Aggrastat®)

Small molecule; reversible. Bolus + infusion.

Setting: Cath lab / CCU

Specialist Agent

Abciximab (ReoPro®)

Monoclonal antibody fragment; irreversible. Used in complex PCI.

Setting: Tertiary centre PCI

Key Indications

High-risk ACS with planned early invasive strategy.
Bail-out situation during PCI (e.g., thrombus，no-reflow).
Elective high-risk PCI (e.g., complex anatomy，left main).

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Major Risk: Significant bleeding risk. Contraindicated in active bleeding，history of intracranial haemorrhage，severe hypertension，or thrombocytopaenia (<100 × 10⁹/L). Renal dose adjustment is required for eptifibatide and tirofiban.

Monitoring

Clinical: Signs of bleeding (gums, bruising，melaena，haematuria)，dyspnoea (ticagrelor)，adherence.
Laboratory: Baseline FBC; monitor for thrombocytopaenia (especially after GP IIb/IIIa inhibitor exposure). Routine platelet function testing is not standard but may be used in specialised centres to assess on-treatment reactivity (e.g., VerifyNow assay).
Pharmacogenomic: Consider CYP2C19 genotyping for poor metabolisers on clopidogrel in high-risk post-PCI settings to guide alternative P2Y12 inhibitor use.

Special Populations

🤰 Pregnancy

Aspirin

Low-dose (100-150 mg) used for pre-eclampsia prophylaxis. Avoid high doses in 3rd trimester.

Clopidogrel / Ticagrelor

Limited data; generally avoided unless benefit clearly outweighs risk (e.g., recent coronary stent). Multidisciplinary decision.

👶 Paediatrics

Aspirin

Used in Kawasaki disease (anti-inflammatory and antiplatelet doses). Reye syndrome risk precludes use for fever/viral illness.

Clopidogrel

PBS-listed for paediatric cardiac conditions (e.g., post-shunt). Dose: 0.2 mg/kg/day (neonates) to 1 mg/kg/day (children).

🏥 Renal Impairment

All agents

Increased bleeding risk. eGFR <30: Avoid aspirin if possible. No clopidogrel/ticagrelor dose adjustment, but monitor closely. GP IIb/IIIa inhibitors require dose reduction (eptifibatide/tirofiban).

🛡️ Elderly (≥75 years)

Prasugrel

Generally contraindicated due to higher bleeding risk.

DAPT

Consider shorter DAPT duration (e.g., 1–6 months) post-ACS/PCI to mitigate bleeding risk.

Aboriginal and Torres Strait Islander Health Considerations

Higher Burden

CVD incidence is 1.5–2 times higher，with earlier onset. Antiplatelet therapy for secondary prevention is of critical importance.

Remote Access

Ensuring reliable supply of medications (e.g., via Section 100 Remote Area Aboriginal Health Services) and timely follow-up for monitoring side effects or bleeding.

Health Literacy

Use pictorial aids，Aboriginal Health Workers，and culturally appropriate education materials to explain the lifelong nature of therapy and signs of bleeding.

Comorbidities

Higher rates of renal disease and diabetes may influence drug choice and increase bleeding risk，requiring careful gastroprotection and monitoring.

📚 References

1. Chew DP, Scott IA, Cullen L, et al. National Heart Foundation of Australia & Cardiac Society of Australia and New Zealand: Australian Clinical Guidelines for the Management of Acute Coronary Syndromes 2016. Heart, Lung and Circulation. 2016;25(9):895-951.
2. Valgimigli M, Bueno H, Byrne RA, et al. 2017 ESC focused update on dual antiplatelet therapy in coronary artery disease. Eur Heart J. 2018;39(3):213-260.
3. American College of Cardiology/American Heart Association. ACC/AHA Guideline for the Management of Patients with Acute Coronary Syndromes (2021).
4. Australian Institute of Health and Welfare (AIHW). Cardiovascular disease in Australia 2023. Cat. no. CVD 86. Canberra: AIHW.
5. NHMRC. Australian Guidelines for the Prevention and Control of Infection in Healthcare (2019). (Context for IE prophylaxis, where relevant).
6. Bhatt DL, Fox KAA, Hacke W, et al. Clopidogrel and Aspirin versus Aspirin Alone for the Prevention of Atherothrombotic Events. N Engl J Med. 2006;354:1706-1717.
7. Wallentin L, Becker RC, Budaj A, et al. Ticagrelor versus Clopidogrel in Patients with Acute Coronary Syndromes. N Engl J Med. 2009;361:1045-1057.
8. The EPIC Investigators. Use of a monoclonal antibody directed against the platelet glycoprotein IIb/IIIa receptor in high-risk coronary angioplasty. N Engl J Med. 1994;330:956-961.
9. RACGP. Smoking, nutrition, alcohol, physical activity (SNAP): A population health guide to behavioural risk factors in general practice. 2nd edition. (Context for primary prevention).
10. Aspirin in the primary prevention of vascular disease: collaborative meta-analysis of individual participant data from randomised controlled trials. Lancet. 2009;373:1849-1860.
11. NHMRC. National Statement on Ethical Conduct in Human Research (2023 updated). (Context for pharmacogenomic testing).
12. The Royal Australian College of General Practitioners. Guidelines for preventive activities in general practice. 10th edition. (Primary prevention context).