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Indiana State Department of Health

Tuberculosis Home > Facts Sheet > MDR TB Multidrug-Resistant TB (MDR TB)

What Is Multidrug-Resistant TB (MDR TB)?

When TB patients do not take their medicine as prescribed, the TB bacteria may become resistant to a certain drug. This means that the drug can no longer kill the bacteria.

Drug resistance is more common in people who

  • were not prescribed the correct medications

  • have spent time with someone with drug-resistant TB disease

  • do not take their medicine regularly

  • do not take all of their prescribed medicine

  • develop TB disease again, after having taken TB medicine in the past

  • come from areas where drug-resistant TB is common (Southeast Asia, Latin America, Haiti, and the Philippines)

Sometimes the bacteria become resistant to the two most important TB drugs; isoniazid and rifampin. This is called multidrug-resistant TB, or MDR TB. This is a very serious problem. People with MDR TB disease must be treated with special drugs that are very expensive. These drugs are not as effective as the first-line drugs, so the treatment time is much longer, usually 18-24 months.  Patients with MDR TB do not respond as quickly as other TB patients. Also, some people with MDR TB disease must see a TB expert who can closely observe their treatment to make sure it is working.

People who have spent time with someone sick with MDR TB disease can become infected with TB bacteria that are resistant to several drugs. If they have a positive skin test reaction, they may be given preventive therapy. This is very important for people who are at high risk of developing MDR TB disease, such as children and HIV-infected people.