]> 2026-07-31T07:51:33+00:00 WBR0737 0 en A The step corresponds to the reaction catalyzed by the enzyme phosphlipase A2. It is inhibited by corticosteroids. B The step corresponds to the reaction catalyzed by the enzyme lipoxygenase. It is inhibited by zileuton, a medication administered for respiratory conditions, such as asthma. C This step corresponds to the reaction catalyzed by cyclooxygenase. It is the main step that is inhibited by aspirin, NSAIDs, and acetaminophen. D This step is secondarily blocked with the use of aspirin. However, aspirin acts at a higher level leading to reduced synthesis of thromboxane A2. E Aspirin does not act at this level of the pathway. Aspirin is an irreversible non-specific inhibitor of prostaglandin synthase, also called cyclooxygenase (COX), enzyme that also acts by acetylation of proteins. The COX enzyme normally leads to the conversion of arachidonic acid into endoperoxides, such as PGG2 and PGH2. With the action of aspirin, the pathway is inhibited; and platelet aggregation is not as effective due to the decreased synthesis of thromboxane A2 downstream in the pathway. Clinically, aspirin is used for its inhibitory effects of platelet aggregation. It is prescribed following percutaneous coronary interventions and is an important medication for secondary prophylaxis among patients with coronary artery disease. Aspirin causes a prolonged bleeding time, reflecting its role on the inhibition of platelet aggregation. Salicylate, the active component of aspirin, is absorbed in the unionized form from the small intestine and is conjugated with glycine in the liver. Peculiarly, aspirin simultaneously causes primary high-anion gap metabolic acidosis and primary respiratory alkalosis; it increases the production of endogenous acids, leading to metabolic acidosis, and has a dose-dependent stimulatory effect of respiratory centers, resulting in hyperventilation and respiratory alkalosis.<br/> '''Educational Objective:''' Aspirin is an irreversible inhibitor of cyclooxygenase enzyme.<br/> '''References:''' Rocca B, Petrucci G. Variability in the responsiveness to low-dose aspirin: pharmacological and disease-related mechanisms. Thrombosis, vol. 2012, Article ID 376721, 11 pages, 2012.<br> First Aid 2014 page 439 Pharmacology C Cardiology 2020-10-28T01:31:50Z 2459150.5637732 WBR0737