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. |
| 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 |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |