What Is Multidrug and Extensively Drug Resistant TB? | American Lung Association

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What Is Multidrug and Extensively Drug Resistant TB?

Multidrug-resistant tuberculosis (MDR TB) is a very dangerous form of tuberculosis. Some TB germs become resistant to the effects of some TB drugs. This happens when TB disease is not properly treated. These resistant germs can then cause a more serious TB disease. The TB disease they cause is much harder to treat because the drugs do not kill the germs. This form of the disease can also be spread to others, just like regular TB. If you have TB, it is important to follow your healthcare provider's instructions for taking your TB medicine so that you will not develop MDR TB.

Extensively drug-resistant TB (XDR TB) is an even more dangerous version of MDR TB. It is resistant to the same drugs as MDR TB, as well as more secondary drugs used to treat MDR TB.  These drugs are often less potent and have more serious side effects. Treatment for XDR TB is much more difficult, expensive, and lasts longer.

Drug-resistant TB can occur when the drugs used to treat TB are misused or mismanaged. For example:

  • When people do not complete the full course of treatment;
  • When healthcare providers prescribe the wrong treatment, the wrong dose, or wrong length of time for taking the drugs;
  • When the supply of drugs is not always available; or
  • When the drugs are of poor quality.

Drug-resistant TB is more common in people who:

  • Do not take their TB drugs regularly
  • Do not take all of their medications for the length of time the doctor recommended
  • Develop TB disease again, after being treated for TB disease in the past
  • Come from areas of the world where drug-resistant TB is common
  • Have spent time with someone known to have drug-resistant TB disease

Learn more about managing TB »


    Approved by Scientific and Medical Editorial Review Panel. Last reviewed October 17, 2016.

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