What is extensively drug-resistant TB (XDR-TB)?
• Extensively drug-resistant tuberculosis (XDR-TB) is a relatively rare type of multi-drug resistant TB (MDR-TB) that is resistant to almost all drugs commonly used to treat drug-susceptible, or regular, TB. TB usually can be treated with a course of four standard drugs also known as first-line drugs. If these drugs are taken incorrectly or prescribed improperly, MDR-TB can develop. MDR-TB can be treated with second-line drugs that are more expensive and often are accompanied by more side effects– treatment is also much longer than treatment for regular TB. If second-line drugs are taken incorrectly or prescribed improperly, XDR-TB can develop, leaving few treatment options available. The World Health Organization (WHO)’s Global Task Force on XDR-TB in October 2006 updated the definition of XDR-TB. The definition also was published in the December 2006 in the Journal of the American Medical Association. XDR-TB is defined as TB that is resistant to at least the two most powerful first-
