ANTIPLATELETS

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ANTIPLATELETS AND FIBRINOLYTICS (THROMBOLYTICS)
ANTIPLATELETS
The formation of platelet aggregates and thrombi in arterial blood may precipitate coronary vasospasm and occlusion, myocardial infarction, and stroke and contribute to atherosclerotic plaque development. Drugs that inhibit platelet function are administered for the relatively specific prophylaxis of arterial thrombosis and for the prophylaxis and therapeutic management of myocardial infarction and stroke. After an infarction or stroke, antiplatelet therapy must be initiated within 2 hours to obtain significant benefit. The antiplatelet drugs are administered as adjuncts to thrombolytic therapy, along with heparin, to maintain perfusion and to limit the size of the myocardial infarction.
The classes of antiplatelets are as follows:
-         Cyclo-oxygenase inhibitors e.g aspirin – They irreversibly inhibit cyclooxygenase (primarily cyclooxygenase-1) in platelets, preventing the formation of thromboxane A2 (TxA2) (a potent vasoconstrictor and trigger in platelet activation and aggregation) and thereby inhibit platelet aggregation.      
-         Inhibitors of ADP-mediated aggregation e.g ticlopidine and clopidogrel. These drugs irreversibly inhibit platelet activation by blocking specific receptors for ADP on the platelet membrane. This action inhibits ADP-induced platelet activation.
-         Phosphodiesterase inhibitors e.g dypiridamole. This drug is a coronary vasodilator and antiplatelet agent. It inhibits platelet cAMP phosphodiesterase activity, thus resulting in decreased platelet aggregation.


ASPIRIN
Review in emdex under the following topics – Therapeutic category, Indications, Mechanism of action (as above), Dosage, Side effects, Contra indications and nursing considerations.

FIBRINOLYTICS (THROMBOLYTICS)
The fibrinolytic system is involved in restricting clot propagation in the blood and in the removal of fibrin as wounds heal. Treatment of patients with fibrinolytic (thrombolytic) drugs that activate the fibrinolytic system is an adjunct to the anticoagulant drugs. The purpose of thrombolytic therapy is rapid lysis of already formed clots.
Fibrinolysis is initiated by the activation of the proenzyme plasminogen (present in clots and in plasma) into plasmin, a protease enzyme not normally present in blood. Plasmin catalyzes the degradation of fibrin. The conversion of plasminogen to plasmin is initiated normally by the plasminogen activators.

Thrombolytic drugs are plasminogen activators. Plasminogen activators e.g streptokinase bind to fibrin on the surface of the clot, activates fibrin-bound plasminogen into plasmin. Plasminthen breaks down the fibrin molecules and the clot dissolves. This causes lysis of formed clots in both arteries and veins and reestablish tissue perfusion.

STREPTOKINASE
Review in emdex under the following topics – Therapeutic category, Indications, Mechanism of action (as above), Dosage, Side effects, Contra indications and nursing considerations.

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