Antituberculosis Drugs – Antimycobacterial Agents

by Pravin Shukle, MD

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    So isoniazid is probably the first drug you need to know. It's very similar to pyridoxine. It inhibits cell wall production in M.tuberclosis. So the bacteria itself is not able to make it cell wall. Resistance develops and it's rapidly developing if you're not using with other medications. It's often due to a point mutation one or two points, one of two points that code for the critical enzymes responsible for making the cell wall. It is not effective against a lot of dominant organisms however. In terms of the toxicity, the biggest thing that we are concerned about is neurotoxicity, which includes restless leg, peripheral neuritis and those thing we treat with vitamin B or pyridoxine. Hepatotoxicity is a concern as well. You can develop abnormal liver function tests. You can develop jaundice and you can develop hepatomegaly. So it's important that you monitor liver function tests regularly. And you do a clinical exam on these patients too. One of the problems that we have with isoniazid is that it interactions with other medications which include carbamazepine, phenytoin and warfarin. So clearly this agent is working through the cytochrome system. One of the other issues that we worry about is hemolysis in those patients who have gluco 6 phosphotate deficiency. So this is an important part of your history before you prescribe this drug. Another agent that we use in TB treatment is rifampin. So rifampin you became very familiar it with when we were talking about inducers and inhibitors of cytochrome. It's very bactericidal side against mycobacterium tuberculosis. Now remember that the drug itself is quite orange colored. So it may discolor urine and it may discolor the feces. And sometimes the patients come in and freaked out because as they are peeing out orange. Just reassure them...

    About the Lecture

    The lecture Antituberculosis Drugs – Antimycobacterial Agents by Pravin Shukle, MD is from the course Antimicrobial Pharmacology. It contains the following chapters:

    • Tubercolosis Agents - First Line Drugs
    • Tubercolosis Agents - Second Line Drugs

    Included Quiz Questions

    1. Start pyridoxine and continue isoniazid.
    2. Discontinue isoniazid immediately, but maintain the other drugs in the regimen.
    3. Observe the patient only, as it is usually a self-limiting side effect.
    4. Switch to the 2nd line regimen of antituberculosis drugs.
    5. Start probenecid and decrease dose of isoniazid.
    1. Rifampin
    2. Isoniazid
    3. Streptomycin
    4. Pyrazinamide
    5. Ethambutol
    1. Rifabutin has less cytochrome induction activity.
    2. Rifabutin also has activity against the HIV virus.
    3. Rifabutin is metabolized in the liver while rifampin is metabolized in the kidney.
    4. Rifampin has a higher risk for renal failure compared to rifabutin.
    5. The HIV virus produces esterases which break down rifampin but not rifabutin.
    1. Non-gouty polyarthralgia
    2. Gout
    3. Visual disturbances
    4. Orange discoloration of urine and feces
    5. Myalgia
    1. Rifampin
    2. Ethambutol
    3. Clarithromycin
    4. Streptomycin
    5. Isoniazid

    Author of lecture Antituberculosis Drugs – Antimycobacterial Agents

     Pravin Shukle, MD

    Pravin Shukle, MD

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