Antiplatelet Drugs (Classification):
- TXA2 synthesis inhibitor:
Low dose aspirin
- Phosphodiesterase inhibitor:
Dipyridamole, cilostazol
- Thienopyridine derivatives (ADP antagonists):
Ticlodipine, clopidogrel
- Gp-IIb/IIIa receptor antagonists
Abciximab, eptifibatide, tirofiban
- Others
PGI2, Bactroban, dazoxiben, clofibrate
Aspirin:
Fig.3: MoA of Aspirin
Dipyridamole:
- Coronary vasodilator and relatively weak antiplatelet drug.
Mechanism of Action:
- Potentiates effect of endogenous prostacyclin.
- In high concentration inhibits Phosphodiesterase, so increases cAMP.
- Dose = 100 mg BD/TDS.
- Used with aspirin to prevent ischemic stroke in patients of TIA.
Ticlodipine and Clopidogrel:
- ADP antagonists, inhibit the binding of ADP to its receptors irreversibly.
- Also, Inhibit fibrinogen induced platelet aggregation without modifying GPIIb/IIIa.
- Synergistic action with aspirin.
- Both are prodrugs have a long duration of antiplatelet effect.
- Clopidogrel a congener of felodipine is safer and better tolerated.
Ticlodipine:
- Adverse effects:
- Diarrrhoea, vomiting, abdominal pain
- Headache, tinnitus, skin rash
- Bleeding, neutropenia, thrombocytopenia
- Dose = 250 mg BD.
Clopidogrel:
- Adverse effects:
- Bleeding most IMP
- Less bone marrow toxicity
- Diarrhoea, epigastric pain, rashes
- Dose = 75 mg OD.
Abciximab:
- Fab fragment of Chimeric monoclonal antibody against GP-IIb/IIIa.
- Used to prevent platelet aggregation in patients having PCI, administered along with aspirin & heparin or LMW heparin.
- The most common A/E is bleeding.
- May cause thrombocytopenia, hypotension, bradycardia.
- Non-antigenic.
Uses of Antiplatelet Drugs:
- Prosthetic heart valves & A-V shunts
- Peripheral vascular disease
- Coronary artery diseases
- Myocardial infarction
- Unstable angina
- Primary & secondary prevention of MI
- Coronary angioplasty, stents, bypass implants
- Cerebrovascular transient ischemic attacks
- Venous thromboembolism.
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