WBR0737

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pharmacology
Sub Category	SubCategory::Cardiology
Prompt	[[Prompt::A 58 year old patient presents to the emergency department (ED) with acute substernal chest pain that radiates to the left shoulder, associated with sweating and nausea. In the ED, an electrocardiogram (ECG) is performed; it shows ST-segment elevation. Blood work-up showed elevated levels of troponin and CPK-MB. The diagnosis of ST-elevation MI is (STEMI) is made. The patient undergoes cardiac catheterization with stent implantation in the left main trunk. The physician prescribes a medication that causes hyperventilation with respiratory alkalosis. Based on the diagram below, at which level does this medication most likely act? ]]
Answer A	AnswerA::A
Answer A Explanation	AnswerAExp::The step corresponds to the reaction catalyzed by the enzyme phosphlipase A2. It is inhibited by corticosteroids.
Answer B	AnswerB::B
Answer B Explanation	AnswerBExp::The step corresponds to the reaction catalyzed by the enzyme lipoxygenase. It is inhibited by zileuton, a medication used in respiratory conditions, like asthma.
Answer C	AnswerC::C
Answer C Explanation	AnswerCExp::This step corresponds to the reaction catalyzed by cycloxygenase. It is inhibited by aspirin, NSAIDs, and acetaminophen.
Answer D	AnswerD::D
Answer D Explanation	AnswerDExp::This step is secondarily stopped with the use of aspirin. However, aspirin acts at a higher level leading to reduced synthesis of thromboxane A2.
Answer E	AnswerE::E
Answer E Explanation	AnswerEExp::Aspirin does not act at this level of the pathway.
Right Answer	RightAnswer::C
Explanation	[[Explanation::Aspirin is an irreversible non-specific inhibitor of cycloxygenase (COX) enzyme that acts by acetylation. The enzyme normally leads to the formation 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. Aspirin causes a prolonged bleeding time, reflecting its role on the inhibition of platelet aggregation. Aspirin stimulates respiratory centers, causing hyperventilation. The latter will lead to a state of respiratory alkalosis and compensatory metabolic acidosis. Educational Objective: Aspirin is an irreversible inhibitor of cycloxygenase enzyme. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::cycloxygenase, WBRKeyword::lipoxygenase, WBRKeyword::aspirin, WBRKeyword::cox, WBRKeyword::arachidonic, WBRKeyword::acid, WBRKeyword::pathway, WBRKeyword::platelet, WBRKeyword::bleeding, WBRKeyword::time, WBRKeyword::acetylation, WBRKeyword::cardiac, WBRKeyword::coronary, WBRKeyword::artery, WBRKeyword::myocardial infarction, WBRKeyword::MI, WBRKeyword::STEMI, WBRKeyword::stent, WBRKeyword::catheterization
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::