Classification of Antiplatelet Drugs (Antithrombotic Drug)

Antiplatelet drugs are essential in the prevention and management of thromboembolic diseases. They inhibit platelet aggregation and reduce the formation of arterial thrombi, which are responsible for conditions such as myocardial infarction, stroke, and peripheral vascular disease. These drugs form a crucial component of antithrombotic therapy.

This blog from Pharmacy Freak outlines the classification, clinical applications, drug of choice, side effects, and current clinical pearls of antiplatelet drugs for students and healthcare professionals.

What is Antiplatelet Drugs

Antiplatelet drugs are agents that interfere with platelet function and prevent platelet aggregation, thereby reducing the formation of thrombi in arteries. They are most effective in preventing arterial thrombosis.

Classification of Antiplatelet Drugs (KD Tripathi)

Fibrinolytics (Thrombolytics):
Streptokinase, Urokinase, Alteplase (rt-PA), Reteplase, Tenecteplase
Antifibrinolytics (Antithrombolytics):
Epsilon amino-caproic acid (EA CA), Tranexamic acid
ANTIPLATELET DRUGS (Antithrombotic Drugs):
- Thromboxane synthesis inhibitor: Aspirin
- Platelet cAMP enhancer: Dipyridamole
- P2Y₁₂ receptor blockers: Ticlopidine, Clopidogrel, Prasugrel
- GP IIb/IIIa antagonists: Abciximab, Eptifibatide, Tirofiban

Classification of Antiplatelet Drugs (General)

Antiplatelet drugs are classified based on their mechanism of action:

Cyclooxygenase (COX) Inhibitors
Mechanism: Inhibit cyclooxygenase-1 (COX-1) in platelets, reducing thromboxane A2 synthesis
Examples:

Aspirin
Use: Primary and secondary prevention of myocardial infarction and stroke
Note: Irreversible inhibition; effect lasts for the life of the platelet (7–10 days)

ADP Receptor (P2Y12) Inhibitors
Mechanism: Block P2Y12 receptors on platelets, preventing ADP-mediated aggregation
Examples:

Clopidogrel
Prasugrel
Ticagrelor
Ticlopidine
Use: Acute coronary syndrome, post-PCI stent placement
Note: Clopidogrel is a prodrug; Ticagrelor is reversible and more potent

Glycoprotein IIb/IIIa Inhibitors
Mechanism: Inhibit final common pathway of platelet aggregation
Examples:

Abciximab
Eptifibatide
Tirofiban
Use: Intravenous agents used during angioplasty or acute coronary syndrome
Note: Most potent class but used only in hospital setting

Phosphodiesterase (PDE) Inhibitors
Mechanism: Increase cAMP in platelets, inhibiting platelet aggregation
Examples:

Dipyridamole
Cilostazol
Use:
Dipyridamole: Combined with aspirin in stroke prevention
Cilostazol: Used in intermittent claudication (peripheral arterial disease)

Protease-Activated Receptor-1 (PAR-1) Antagonists
Mechanism: Block thrombin-induced platelet aggregation
Example:

Vorapaxar
Use: Secondary prevention in patients with prior MI or PAD
Note: Used as add-on therapy; high bleeding risk

Uses

Antiplatelet drugs are used in:

Acute coronary syndrome (NSTEMI, STEMI)
Secondary prevention after myocardial infarction
Post-percutaneous coronary intervention (PCI) with stent placement
Ischemic stroke and transient ischemic attack (TIA)
Peripheral arterial disease
Prevention of thromboembolism in atrial fibrillation (when anticoagulants are contraindicated)
Graft or shunt thrombosis prevention
Prevention of clotting in hemodialysis machines or during procedures

Drug of Choice Highlights

Primary prevention of cardiovascular events – Low-dose Aspirin
Acute coronary syndrome – Dual antiplatelet therapy (Aspirin + Clopidogrel or Ticagrelor)
Post-stenting (PCI) – Aspirin + P2Y12 inhibitor (e.g., Clopidogrel for at least 1 year)
Secondary stroke prevention – Aspirin or Aspirin + Dipyridamole
Peripheral artery disease with claudication – Cilostazol
Aspirin intolerance – Clopidogrel
High-risk percutaneous interventions – Abciximab (IV)

Side Effects

Aspirin – Gastric irritation, peptic ulcers, bleeding, hypersensitivity
Clopidogrel – Diarrhea, rash, thrombotic thrombocytopenic purpura (rare)
Ticagrelor – Dyspnea, bleeding, bradycardia
Prasugrel – Higher bleeding risk, contraindicated in stroke or elderly patients
Glycoprotein IIb/IIIa inhibitors – Bleeding, thrombocytopenia
Dipyridamole – Headache, dizziness, hypotension
Cilostazol – Palpitations, headache, contraindicated in heart failure
Vorapaxar – Serious bleeding, not for use in patients with stroke or TIA history

Updated Clinical Pearls

Aspirin is still the most widely used and cost-effective antiplatelet agent for both primary and secondary prevention.
Dual antiplatelet therapy (DAPT) with aspirin and a P2Y12 inhibitor is standard for 12 months post-stent placement.
Ticagrelor and Prasugrel are more potent than Clopidogrel but carry a higher bleeding risk.
Cilostazol improves walking distance in patients with intermittent claudication and has antiplatelet properties.
Vorapaxar is a novel agent reserved for high-risk patients and is not routinely used due to bleeding concerns.
Genetic testing may be considered in poor responders to Clopidogrel due to CYP2C19 polymorphisms.

References

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