WBR0757

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pharmacology
Sub Category	SubCategory::Pulmonology
Prompt	[[Prompt::A 23 year old male patient, previously healthy, presents to the physician's office complaining 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. He dilutes the powder in saline containing 0.4% phenol using a sterile technique. For safety purposes also, the physician puts on the table another medication in case of serious side effects occur. Which medication is most likely put nearby on the table during the procedure?]]
Answer A	AnswerA::Atropine
Answer A Explanation	AnswerAExp::Atropine is an anti-muscarinic agent that aids in bronchodilation in case severe bronchoconstriction occurs.
Answer B	AnswerB::Salmetrol
Answer B Explanation	AnswerBExp::Long-acting B2 agonists are generally helpful, but may not be very useful in such 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 may cross 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 may help 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 that contains 0.4% phenol using sterile technique. Methacholine is a synthetic derivative of acetylcholine, but is metabolized much slower by cholinesterase. Its effect can nonetheless be blocked or reduced by atropine or other anticholinergic medications. For safety purposes, oxygen and medications that decrease the degree of bronchoconstriction induced by methacholine must be present in the testing area nearby at all times. These medications may include any of the following: Epinephrine, atropine, albuterol, ipratropium. However, serious adverse effects are considered rare during methacholine challenge test, but should still be considered regardless of how rare they might be. There are some contraindications to the metacholine challenge test, including severe airflow limitations, cardiovascular conditions, like myocardial infarction or stroke within 3 months, uncontrolled hypertension or aortic aneurysm. Other relative contraindications include: Moderate airflow limitations, pregnancy or nursing mothers, use of cholinesterase inhibitors, and inability to perform acceptable spirometry. Educational Objective: Atropine, or similar bronchodilators, like epinephrine, B2 agonists, or ipratropium, and oxygen must always be available during methacholine challenge testing for safety purposes in case any serious bronchoconstrictive adverse event occurs. Reference: 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. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::atropine, WBRKeyword::methacholine, WBRKeyword::challenge, WBRKeyword::test, WBRKeyword::asthma, WBRKeyword::exercise, WBRKeyword::induced, WBRKeyword::bronchoconstriction, WBRKeyword::bronchodilation, WBRKeyword::safety, WBRKeyword::side, WBRKeyword::effect, WBRKeyword::serious, WBRKeyword::adverse, WBRKeyword::event
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