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The page below is a sample from the LabCE course Antiplatelet and Anticoagulant Pharmacology for the Laboratory Professional. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Aspirin and other Nonsteroidal Anti-Inflammatory Drugs (NSAIDs)

  • Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) are drugs used in many different medical conditions, from pain to improving mortality after a heart attack or stroke.
  • Mechanism of action: Normally, arachidonic acid is converted to thromboxane A2 due to the activity of the enzyme cyclooxygenase (COX). As discussed in the first section of this course, thromboxane A2 stimulates platelet aggregation during the formation of the platelet plug. Aspirin irreversibly inhibits the enzyme COX, leading to decreased production of thromboxane A2 and decreased platelet aggregation. Since platelets do not have a nucleus, they do not have the means of producing more COX enzyme to overcome the effects of aspirin. Thus, aspirin inhibits platelets for the remainder of their life-span, which could be up to ten days.
  • Other NSAIDs only temporarily inhibit COX and the inhibition of thromboxane A2 production lasts hours, instead of days.
  • Use: Aspirin is regularly used in patients who have had heart attacks and strokes or may have a heart attack or stroke. Platelet aggregation plays a role in the thrombosis of coronary and cerebral arteries.
  • Laboratory measurement: Several methods of measuring the response to aspirin are available. Aspirin does not decrease platelet count, but instead changes platelet function. Thus, you would expect an increase in bleeding in the bleeding time test. Various platelet aggregation assays are available and can be performed to determine the in vitro response of platelets to various platelet agonists. Platelets that are responding appropriately to aspirin should show decreased aggregation. An ELISA also exists for 11-dehydrothromboxane B2 (11-dTXB2), a metabolite of thromboxane A2. The level 11-dTXB2 is proportional to the amount of thromboxane A2 and thus platelet activity.
  • Toxicity: Aspirin has many potential side effects, from tinnitus to kidney injury. It also leaves the gastric lining vulnerable to stomach acid and stomach upset is a common complaint.