{"id":4079,"date":"2024-07-10T16:02:00","date_gmt":"2024-07-10T16:02:00","guid":{"rendered":"https:\/\/www.osmosis.org\/blog\/?p=4079"},"modified":"2025-10-01T11:38:22","modified_gmt":"2025-10-01T19:38:22","slug":"usmle-step-2-question-of-the-day-mycolic-acid","status":"publish","type":"post","link":"https:\/\/www.osmosis.org\/blog\/usmle-step-2-question-of-the-day-mycolic-acid","title":{"rendered":"USMLE\u00ae Step 2 Question of the Day: Mycolic acid"},"content":{"rendered":"<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_80 ez-toc-wrap-center counter-hierarchy ez-toc-counter ez-toc-custom ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">In This Article<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Toggle Table of Content\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-2-question-of-the-day-mycolic-acid\/#The_correct_answer_to_todays_USMLE%C2%AE_Step_2_CK_Question_is%E2%80%A6\" >The correct answer to today&#8217;s USMLE\u00ae Step 2 CK Question is&#8230;<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-2-question-of-the-day-mycolic-acid\/#Incorrect_Answer_Explanations\" >Incorrect Answer Explanations<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-2-question-of-the-day-mycolic-acid\/#Main_Explanation\" >Main Explanation<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-2-question-of-the-day-mycolic-acid\/#Major_Takeaway\" >Major Takeaway<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-2-question-of-the-day-mycolic-acid\/#References\" >References<\/a><\/li><\/ul><\/nav><\/div>\n\n<p class=\"wp-block-paragraph\"><strong><em>Test your knowledge with this USMLE Step 2 Question of the Day. A 37-year-old man with a history of hypertension and frequent travel to tuberculosis-endemic regions presents for a routine visit. He has no symptoms, but his tuberculin skin test and interferon-gamma assay are positive. The patient is initiated on isoniazid to treat latent tuberculosis. Which additional medication should be administered to prevent potential side effects?<\/em><\/strong><br><strong><em><br><\/em><\/strong>A 37-year-old man comes to his outpatient provider for a routine visit. The patient is feeling well and has no symptoms. Past medical history is notable for hypertension. He works as a consultant and frequently travels overseas to meet with clients in China and India. Temperature is 37.0\u00b0C (98.6\u00b0F), blood pressure is 157\/86 mmHg, and pulse is 75\/min. Physical examination is unremarkable. A purified protein derivative injection is performed. After two days, a wheal measuring 16 mm in diameter is present at the injection site. An interferon-gamma test is performed and returns positive. The patient is initiated on a medication that inhibits the bacterial synthesis of mycolic acid. Which of the following additional medications should be administered to this patient?\u00a0<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>A.&nbsp;Ethambutol&nbsp;<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>B.&nbsp;Vitamin B1&nbsp;<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>C.&nbsp;Pyrazinamide<br><\/strong><br><strong>D.&nbsp;Vitamin B6<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>E.&nbsp;Streptomycin&nbsp;<\/strong><\/p>\n\n\n\n<p class=\"has-text-align-center wp-block-paragraph\"><em>Scroll down for the correct answer!<\/em><\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"The_correct_answer_to_todays_USMLE%C2%AE_Step_2_CK_Question_is%E2%80%A6\"><\/span>The correct answer to today&#8217;s USMLE\u00ae Step 2 CK Question is&#8230;<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>D.&nbsp;<\/strong><strong>Vitamin B6<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Before we get to the&nbsp;<strong>Main Explanation<\/strong>, let&#8217;s see why the answer wasn&#8217;t A, B, C, or E. Skip to the bottom if you want to see the correct answer right away!<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Incorrect_Answer_Explanations\"><\/span>Incorrect Answer Explanations<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>A.\u00a0Ethambutol<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Incorrect:<\/strong>&nbsp;Ethambutol is a medication used to treat active tuberculosis. Ethambutol works by inhibiting arabinogalactan synthesis, as opposed to mycolic acid synthesis. In contrast, this patient has evidence of latent tuberculosis since he remains asymptomatic despite having a positive purified protein derivative (PPD) test and interferon-gamma assay.&nbsp;<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>B.&nbsp;Vitamin B1<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Incorrect:&nbsp;<\/strong>Vitamin B1, also known as thiamine, can be administered to patients with chronic alcohol abuse or other forms of malnutrition to reduce the risk of Wernicke encephalopathy. However, this patient does not have a history of malnutrition. Furthermore, he was started on isoniazid to treat latent tuberculosis and would more likely require vitamin B6 supplementation.&nbsp;<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>C.&nbsp;Pyrazinamide&nbsp;<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Incorrect:&nbsp;<\/strong>Pyrazinamide is a medication used to treat active tuberculosis. In contrast, this patient has latent tuberculosis since he remains asymptomatic despite having a positive purified protein derivative (PPD) test and interferon-gamma assay.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>E.&nbsp;Streptomycin&nbsp;<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Incorrect:&nbsp;<\/strong>Streptomycin is an aminoglycoside that can be used with other medications to treat miliary tuberculosis and&nbsp;Mycobacterium tuberculosis&nbsp;meningitis. Streptomycin works by inhibiting the bacterial 30S ribosomal subunit and preventing protein synthesis instead of inhibiting mycolic acid synthesis.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Main_Explanation\"><\/span>Main Explanation<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">This patient has traveled to tuberculosis-endemic regions and has a positive tuberculin skin test and interferon-gamma assay but remains asymptomatic. He likely has&nbsp;latent tuberculosis&nbsp;and was appropriately initiated on isoniazid therapy. Patients on isoniazid should also receive&nbsp;vitamin B6 (pyridoxine) supplementation.&nbsp;<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Isoniazid&nbsp;can be used alone to treat latent tuberculosis or in combination with other medications to treat active tuberculosis. The medication inhibits&nbsp;mycolic acid synthesis, an essential component of the mycobacterial cell wall. It also inhibits&nbsp;mycobacterial peroxidase, which leads to hydrogen peroxide accumulation within mycobacteria inducing cellular damage.&nbsp;&nbsp;<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Isoniazid use may lead to pyridoxine deficiency, manifest with sideroblastic anemia, encephalopathy, ataxia, dizziness, and&nbsp;peripheral neuropathy. Fortunately, these side effects can be prevented with pyridoxine supplementation. As a result, patients taking isoniazid should receive&nbsp;daily pyridoxine.&nbsp;&nbsp;<\/p>\n\n\n\n<figure class=\"wp-block-image aligncenter size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"487\" height=\"272\" src=\"https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/07\/Isoniazid-step-2.png\" alt=\"ISONIAZID\nSide Effects:\n* Rash\n* Fever\n* Systemic Lupus Erythematosus (Drug-induced SLE)\n* Vitamin B6 deficiency\n\nOverdose\n* Seizures\n* Metabolic acidosis\n* Coma\n\nAntidote for:\n* Anemia\n* Dizziness\n* Ataxia\n* Encephalopathy\n* Peripheral neuropathy\n\nCan be prevented with pyridoxine or Vitamin B6\" class=\"wp-image-7610\" srcset=\"https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/07\/Isoniazid-step-2.png 487w, https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/07\/Isoniazid-step-2.png?resize=300,168 300w\" sizes=\"auto, (max-width: 487px) 100vw, 487px\" \/><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Major_Takeaway\"><\/span>Major Takeaway<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Isoniazid&nbsp;is used to treat tuberculosis and can cause vitamin B6 (pyridoxine) deficiency. Patients on isoniazid should receive&nbsp;daily pyridoxine supplementation.&nbsp;<\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"References\"><\/span>References<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>O\u2019Connor, C., Brady, M.F. (2020) \u201cIsoniazid\u201d.&nbsp;StatPearls [Internet]. Web Address:&nbsp;<a href=\"https:\/\/www.ncbi.nlm.nih.gov\/books\/NBK557617\/\" target=\"_blank\" rel=\"noreferrer noopener\">https:\/\/www.ncbi.nlm.nih.gov\/books\/NBK557617\/<\/a>.&nbsp;<\/li>\n\n\n\n<li>Snider Jr., D.E. (1980) Pyridoxine supplementation during isoniazid therapy.&nbsp;Tubercle. 61(4), 191-196. Doi: 10.1016\/0041-3879(80)90038-0.&nbsp;<\/li>\n\n\n\n<li>Sotgiu, G., Centis, R., D\u2019ambrosio, L., Migliori, G.B. (2015) Tuberculosis treatment and drug regimens.\u00a0Cold Spring Perspectives in Medicine. 5(5), a017822. Doi: 10.1101\/cshperspect.a017822.\u00a0<\/li>\n<\/ul>\n\n\n\n<figure class=\"wp-block-image size-large\"><a href=\"https:\/\/osmosis.org\/plans\/\" target=\"_blank\" rel=\"noreferrer noopener\"><img loading=\"lazy\" decoding=\"async\" width=\"700\" height=\"250\" src=\"https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2025\/02\/Blog_Display_Ads_GENERAL2_2023.png?w=700\" alt=\"\" class=\"wp-image-5441\" srcset=\"https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2025\/02\/Blog_Display_Ads_GENERAL2_2023.png 700w, https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2025\/02\/Blog_Display_Ads_GENERAL2_2023.png?resize=300,107 300w\" sizes=\"auto, (max-width: 700px) 100vw, 700px\" \/><\/a><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\"><em><strong>Want more \u00a0USMLE\u00ae Step 2 CK practice questions?\u00a0Try Osmosis by Elsevier today! Access your\u00a0<a href=\"https:\/\/www.osmosis.org\/login?type=create\" target=\"_blank\" rel=\"noreferrer noopener\">free trial<\/a>\u00a0and find out why millions of current and future clinicians and caregivers love learning with us.<\/strong><\/em><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Test your knowledge with this USMLE Step 2 Question of the Day. A 37-year-old man with a history of hypertension and frequent travel to tuberculosis-endemic regions presents for a routine visit. He has no symptoms, but his tuberculin skin test and interferon-gamma assay are positive. The patient is initiated on isoniazid to treat latent tuberculosis. [&hellip;]<\/p>\n","protected":false},"author":202,"featured_media":4080,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_post_was_ever_published":false},"categories":[27,20,16,1370,45],"tags":[],"class_list":["post-4079","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-medicine","category-exam-prep","category-do","category-step-2-questions","category-step-2"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v23.6 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>USMLE\u00ae Step 2 Question of the Day: Mycolic acid - Osmosis Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.osmosis.org\/blog\/usmle-step-2-question-of-the-day-mycolic-acid\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"USMLE\u00ae Step 2 Question of the Day: Mycolic acid - Osmosis Blog\" \/>\n<meta property=\"og:description\" content=\"Test your knowledge with this USMLE Step 2 Question of the Day. A 37-year-old man with a history of hypertension and frequent travel to tuberculosis-endemic regions presents for a routine visit. He has no symptoms, but his tuberculin skin test and interferon-gamma assay are positive. The patient is initiated on isoniazid to treat latent tuberculosis. [&hellip;]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.osmosis.org\/blog\/usmle-step-2-question-of-the-day-mycolic-acid\" \/>\n<meta property=\"og:site_name\" content=\"Osmosis Blog\" \/>\n<meta property=\"article:published_time\" content=\"2024-07-10T16:02:00+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2025-10-01T19:38:22+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.osmosis.org\/blog\/wp-content\/uploads\/sites\/2\/2024\/09\/usmle-mycolic-acid.webp\" \/>\n\t<meta property=\"og:image:width\" content=\"1080\" \/>\n\t<meta property=\"og:image:height\" content=\"1080\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/webp\" \/>\n<meta name=\"author\" content=\"Marina Horiates Kerekes, MD &amp; Team\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":[\"Article\",\"BlogPosting\"],\"@id\":\"https:\/\/www.osmosis.org\/blog\/usmle-step-2-question-of-the-day-mycolic-acid#article\",\"isPartOf\":{\"@id\":\"https:\/\/www.osmosis.org\/blog\/usmle-step-2-question-of-the-day-mycolic-acid\"},\"author\":{\"name\":\"Marina Horiates Kerekes, MD &amp; 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