Topic Overview

Multidrug-resistant tuberculosis (MDR-TB) occurs when the bacteria are resistant to at least isoniazid and rifampin. This means that these medicines are unable to kill the bacteria. The reasons antibiotic resistance occurs include:

• Medicine treatment failure. Failure to complete the entire course of treatment is the major cause of multidrug-resistant TB. If all of the medicines prescribed are not taken as directed, the weaker bacteria are killed, but some stronger, more resistant bacteria survive. These resistant bacteria can grow and cause TB disease that is difficult to cure.
• Inadequate TB control measures. People with multidrug-resistant TB disease can infect others with drug-resistant bacteria. This has happened in prisons, hospitals, and homeless shelters.

People who have resistant disease are at increased risk for dying of TB, especially if they also are infected with the human immunodeficiency virus (HIV). People who are at highest risk for developing multidrug-resistant TB are those who:

• Have a weakened immune system, such as people who are infected with HIV, have AIDS, or have cancer.
• Have been in close contact with a person who is infected with multidrug-resistant TB.
• Do not take their prescribed medicine regularly or do not take all of their medicine.
• Develop TB disease again after having taken TB medicine in the past.
• Come from areas where TB is common, such as Southeast Asia, Africa, or Latin America.

To reduce the problem of drug resistance, doctors now use the following guidelines to treat all people who have resistant TB:¹

• Almost everyone begins treatment of TB with four different medicines, which are taken until a culture test shows no bacteria. Then, two medicines are taken for 4 to 7 months. Young children and pregnant women may begin TB treatment using only three medicines.
• Everyone who has TB is tested to learn which medicines will kill the TB-causing bacteria (antibiotic sensitivity testing).
• A health professional must watch the person take every dose of medicine. This is called directly observed therapy (DOT) and may mean a daily office or home visit. DOT does help make sure that all of the medicines are taken, and it has raised cure rates.
• Whenever possible, a person is treated at a center that specializes in treating multidrug-resistant TB.

A rare type of MDR-TB is called extensively drug-resistant tuberculosis (XDR-TB). This type of TB is resistant to isoniazid, rifampin, and several other medicines used to treat TB.