Platelet-inhibiting drugs

FIGURE 4.1 The role of platelets in arresting tissue injury. ADP = adenosine diphosphate. 

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Activation of platelets is considered an essential process for arterial thrombosis. Thus, treatment with platelet-inhibiting drugs such as aspirin and ticlopidine or clopidogrel is indicated in patients with transient ischemic attacks and strokes or unstable angina and acute myocardial infarction. In angina and infarction, these drugs are often used in conjunction with -blockers, calcium channel blockers, and fibrinolytic drugs. 

PLATELET-INHIBITING DRUGS A combination of acetylsalicylic acid and dipyridimole... 

Aspirin covalently modifies COX-1 and COX-2, irreversibly inhibiting COX activity. This is an important distinction from all the NSAIDs because the duration of aspirin s effects is related to the turnover rate of COX in different target tissues. The duration of effect of nonaspirin NSAIDs, which competitively inhibit the active sites of the COX enzymes, relates more directly to the time course of drug disposition. The importance of enzyme turnover in relief from aspirin action is most notable in platelets, which, being anucleate, have a markedly limited capacity for protein synthesis. Thus, the consequences of inhibition of platelet COX (COX-1) last for the lifetime of the platelet. Inhibition of platelet COX-1-dependent TXA formation, therefore, is cumulative with repeated doses of aspirin (at least as low as 30 mg/day) and takes roughly 8-12 days (the platelet turnover time) to recover once therapy has been stopped. 

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