Multidrug-resistant tuberculosis (MDR TB) is a form of tuberculosis that is resistant to two or more of the primary drugs (isoniazied and rifampin) used for the treatment of tuberculosis. Extensively drug-resistant TB (XDR TB) is TB resistant to at least isoniazid and rifampin among the first-line anti-TB drugs and is resistant to any fluoroquinolone and at least one of the three second-line injec
table drugs.1 Resistance to one or several forms of treatment occurs when the bacteria develops the ability to withstand antibiotic attack and relays that ability to its offspring. Since that entire strain of bacteria inherits this capacity to resist the effects of the various treatments, resistance can spread from one person to another. On an individual basis, however, inadequate treatment or improper use of the anti-tuberculosis medications remains an important cause of drug-resistant tuberculosis. Drug-resistant TB is difficult and costly to treat and can be fatal. Statistics below pertain only to cases with drug susceptibility testing done and no previous history of TB. In 2011, the CDC reported that 9.2 percent of tuberculosis cases in the U.S. were resistant to isoniazid, the first-line drug used to treat TB.2
The CDC also reported that 1.3 percent of tuberculosis cases in the U.S. were resistant to both isoniazid and rifampin.
