WBR0757

Author	[[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pharmacology
Sub Category	SubCategory::Pulmonology
Prompt	[[Prompt::A 23-year-old man with no past medical history presents to the physician's office with complaints of difficulty breathing during exercise. The patient denies similar symptoms at rest. The physician suspects exercise-induced asthma and decides to perform a bronchoprovocation challenge test using a crystalline powder. Using a sterile technique, he dilutes the powder in saline containing 0.4% phenol using a sterile technique. For safety precautions, the physician prepares another drug and puts it on the table to manage any potential serious adverse event that may occur with the bronchoprovocation challenge test. Which drug is most likely put nearby on the table during the procedure?]]
Answer A	AnswerA::Atropine
Answer A Explanation	[[AnswerAExp::Atropine is a fast-acting, antimuscarinic, bronchodilating agent that may reverse methacholine-induced severe bronchoconstriction.]]
Answer B	AnswerB::Salmetrol
Answer B Explanation	[[AnswerBExp::Long-acting B2 agonists are not very useful in acute bronchoconstrictive situations.]]
Answer C	AnswerC::Edrophonium
Answer C Explanation	[[AnswerCExp::Edrophonium is an anticholinesterase that may help in the diagnosis of myasthenia gravis.]]
Answer D	AnswerD::Physostigmine
Answer D Explanation	[[AnswerDExp::Physostigmine is an anticholinesterase that crosses the blood-brain-barrier. It is a cholinomimetic and may be used to reverse the effects of atropine.]]
Answer E	AnswerE::Norepinephrine
Answer E Explanation	[[AnswerEExp::Norepinephrine is generally not useful in bronchoconstriction because unlike epinephrine, it lacks B2 activity.]]
Right Answer	RightAnswer::A
Explanation	[[Explanation::The patient is undergoing the methacholine challenge test that helps in the diagnosis of asthma. Methacholine is a crystalline powder that is stored at cold temperatures before use. As described in the vignette, it is mixed with saline containing 0.4% phenol using a sterile technique. Methacholine is a synthetic derivative of acetylcholine that is metabolized much slower than acetylcholine by cholinesterase. Its effect can nonetheless be blocked or reduced by atropine or other anticholinergic agents with bronchodilating action. Serious adverse events are considered rare during methacholine challenge test, but precaution should still be considered regardless of how rare they are. For safety precautions, oxygen and bronchodilators must always be present nearby in the testing area at all times during the procedure. Bronchodilators may be any of epinephrine, atropine, albuterol, or ipratropium. Contraindications to the methacholine challenge test include severe airflow limitations and cardiovascular conditions (such as history of prior myocardial infarction, recent stroke, uncontrolled hypertension, or aortic aneurysm). Other relative contraindications include moderate airflow limitations, pregnancy or nursing, use of cholinesterase inhibitors, and inability to perform acceptable spirometry. Educational Objective: Either atropine or similar fast-acting bronchodilators (epinephrine, B2 agonists, or ipratropium) along with oxygen supplementation must always be available and ready to prevent serious bronchoconstrictive adverse events during methacholine challenge testing. References: Crapo RO, Casaburi R, Coates AL, et al. Guidelines for methacholine and exercise challenge testing - 1999. This official statement of the American Thoracic Society was adopted by the ATS Board of Directors, July 1999. Am J Respir Crit Care Med. 2000;161(1):309-29. First Aid 2014 page 614]]
Approved	Approved::Yes
Keyword	WBRKeyword::Atropine, WBRKeyword::Methacholine challenge test, WBRKeyword::Asthma, WBRKeyword::Exercise-induced asthma, WBRKeyword::Shortness of breath, WBRKeyword::Dyspnea, WBRKeyword::Oxygen, WBRKeyword::Safety precautions, WBRKeyword::Procedure, WBRKeyword::Bronchodilator, WBRKeyword::Anticholinergics
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