Asprin is not given in a patient who is already on heparin because aspirin causes:: (A) Platelet dysfunction, (B) Aspirin inhibits the action of heparin, (C) Enhanced hypersensitivity of heparin, (D) Therapy of heparin cannot be monitored
Answer is A. Aspirin inactivates cyclo-oxygenase by irreversible acetylation of the enzyme and thereby inhibit the synthesis of thromboxane A2. Thromboxane A2 normally promotes platelet aggregation. This COX inhibition lasts for 7 - 10 days till fresh platelets are formed. From medical pharmacology padmaja 4th edition Page no 344