Antiplatelet Agents

A visual summary of antiplatelet agents.

COX inhibitors Aspirin-Thrombotic events happen when platelet rich thrombus forms in atheromatous arteries and occludes circulation.Irreversibly inhibits Platelet Cyclo-oxygenase (Key enzyme in platelet biosynthesis pathway of TxA2).Thromboxane A2 ( platelet activator & potent vasoconstrictor).Prolongation of skin bleeding time Fails to prevent aggregation induced by thrombin Only partially inhibits that induced by ADP and high dose collagen Effect lasts about 10 days ( lifespan of platelet ) Coagulation tests are unaltered. Adverse effects-Gastric erosion and GI bleeding (due to inhibition of prostaglandin synthesis ) GI effects are dose related Hypersensitivity reactions as -eg Exacerbation of asthma ( 1 in 20 asthma sufferers can be sensitive ) Intracranial haemorrhage

ADP Antagonists - Platelet adenosine diphosphate P2Y (12) receptor antagonists

THIENOPYRIDINE DERIVATIVES Block binding of ADP to its platelet receptor ( ADP is powerful inducer of platelet aggregation ) Interfere with ADP mediated activation of glycoprotein IIb-IIIa complex Irreversibly inhibit platelet aggregation No effect on prostaglandin metabolism Do not affect coagulation profile ( ie PT and PTT minitoring is not required )

Clopidogrel-similar safety and tolerability and effectiveness as aspirin Used in patients who cannot tolerate aspirin Most common SE is bleeding Advantageous in combination with aspirin...