Case Studies – Antimycobacterial Agents

by Pravin Shukle, MD

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    00:00 Let's move on to a question.

    00:03 A woman from a first nations reserve in western Alaska presents with cough with flecks of blood in her green sputum.

    00:10 She has a three month history of fatigue, weight loss and poor appetite.

    00:15 Her sputum is identified with microbaterium tuberculosis.

    00:18 There has been one historical case from her reserve without resistance patterns.

    00:24 The appropriate course of action would be A. Initiate isoniazid, rifampin, pyrazinamide and streptomycin.

    00:33 B. Initiate rifampin to treat for 9 months.

    00:37 C. Initiate isoniazid for 18 months.

    00:41 D. Initiate isoniazid, rifampin and pyrazinamide.

    00:46 If the organisms are fully susceptible, pyrazinamide can be stopped in two months.

    00:51 Or E. Initiate pyrazinamide for 18 months.

    00:57 Okay you chose D and that's correct.

    01:01 Now this is a hard question but let's just go through it so that you understand the concept.

    01:07 And when you to the exam you'll feel much more confident answering these kinds of questions.

    01:12 So in areas with less than 4% resistance isoniazid, a three drug combination is actually reasonable.

    01:21 Now the questions on TV will not focus on your intimate knowledge of each of it's drugs, but on the uses and indications.

    01:29 If the patient had come from say an area of high endemic resistance, like South Asia or South East Asia, Somalia or China, a 4 drug regimen is appropriate.

    01:39 Now some people are advocating the 2 drug approach with just isoniazid and rifampin for 9 or 18 months.

    01:47 This is not unreasonable and could be correct.

    01:50 But the reality is that we use the 3 drug combination in almost all cases.

    01:55 So if you are caught with a question that gives you this choice and no other, then the 2 drug approach would be the answer.

    02:02 But in most cases you're going to be given an option for 3 drug approach.

    02:06 And that would probably be the right answer unless they specifically mention resistance.

    02:11 Single drug treatment of active TB is never a reasonable choice on exams or in the TB clinic.

    02:20 Now let's go on to the next question.

    02:24 The woman from question one received the appropriate treatment as part of the regimen, the CDC consultant also added pyridoxine or vitamin B6 to her regimen.

    02:35 What was the purpose of pyridoxine? Now if you're not sure what the first question was, it's just dealing with a woman from a reserve in Alaska who is found to have TB in the sputum.

    02:49 Let's take a look at our choices.

    02:51 A. Pyridoxine will reduce the risk of pulmonary scarring during treatment.

    02:55 B. Pyridoxine will reduce the risk of hepatotoxicity during treatment.

    03:01 C. Pyridoxine will reduce the risk of dental erosions during treatment.

    03:07 D. Pyridoxine will reduce the risk of arrhythmia during treatment.

    03:11 or E. Pyridoxine will reduce the risk of neurotoxicity during treatment.

    03:17 And the answer of course is E.

    03:22 This is a third question in the a string of two.

    03:28 The woman from question 1 was on oral contraceptives.

    03:30 If you've lost two questions, just be aware that she was started on 3 drug regiment for TB and she lives on a reserve with no worrisome resistance patterns.

    03:40 She does not wish to get pregnant.

    03:43 Which drug is most likely to interfere with the oral contraceptive agent? Is it A. Ethambutol, B. Isoniazid, C. Rifampin, D. Pyridoxine or E. Pyrazinamide.

    03:59 Good for you, you chose rifampin.

    04:02 Now rifampin is an important thing to think about.

    04:06 Because rifampin is the prototypical cytochrome inducer.

    04:10 And it is the drug that we talk about, when we're talking about multidrug interactions.

    04:15 So rifampin is going to be the answer in that case.

    04:22 Let's go on to the next question.

    04:24 A 36 year old HIV positive male is tachypneic and hypoxic.

    04:30 His chest X-ray shows right middle lobe infection.

    04:33 He was diagnosed with microbaterium avium complex or MAC.

    04:38 The appropriate treatment is one of the following.

    04:41 Is it A) Clarithromycin with rifabutin.

    04:44 Is it B) Azithromycin with rifabutin.

    04:47 Is it C) Isoniazid with rifabutin.

    04:51 Is it D) Azithromycin or Clarithromycin with ethambutol and rifabutin.

    04:57 Or is it E) Ethambutol, streptomycin, rifampin, isoniazid and penicillin.

    05:04 Good, you chose D.

    05:07 You can choose either azithromycin or clarithromycin with ethambutol and rifabutin as the second and third agents in the treatment.

    05:18 Microbaterium avium complex or MAC was actually first described as Lady Windermere syndrome.

    05:26 Now who is Lady Windermere.

    05:28 She was a character in Oscar Wilde's play.

    05:30 She was one of these very proper people who wouldn't cough or wouldn't expectorate.

    05:35 And actually it was surprisingly common in these women to see right middle lobe pneumonia because it is cough of the junk that was in their lungs.

    05:43 MAC made a come back in the post-AIDS era.

    05:46 It is treated with a 3 drug regimen that includes a macrolide, ethambutol and rifabutin.

    05:52 Infections from other bacteria like microbacterium ulcerans or microbacterium marinum are treated with similar drugs or other antibiotics that are usually not a horribly symptomatic disease.

    06:05 That's it.

    06:07 You completed a very tough section.

    06:09 I'm really proud of you.

    06:11 Now go up to that exam and show them what you know.

    About the Lecture

    The lecture Case Studies – Antimycobacterial Agents by Pravin Shukle, MD is from the course Antimicrobial Pharmacology.

    Included Quiz Questions

    1. B6 (pyridoxine)
    2. B1 (thiamine)
    3. B2 (riboflavin)
    4. B3 (niacin)
    5. B9 (folate)
    1. Drug interactions (CYP-450 inducer)
    2. Hair loss
    3. Photosensitivity
    4. Enamel hypoplasia
    5. Tubulointerstitial nephritis
    1. A 4-drug regimen should be used for patients from areas of high endemic resistance.
    2. A 3-drug regimen is appropriate in an area with 8% resistance to INH.
    3. Ethambutol can be used as a monotherapy against tuberculosis.
    4. Pyridoxine supplementation increases hepatotoxicity risk.
    5. Azithromycin and rifabutin are both effective against M. tuberculosis.

    Author of lecture Case Studies – Antimycobacterial Agents

     Pravin Shukle, MD

    Pravin Shukle, MD

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