Extensively drug-resistant tuberculosis (XDR-TB) is a severe form of tuberculosis (TB) caused by Mycobacterium tuberculosis bacteria that are resistant to at least four of the core anti-TB drugs. These include isoniazid and rifampicin (which define multi-drug resistant TB (MDR-TB)), any fluoroquinolone, and at least one of the three second-line injectable drugs (amikacin, kanamycin, or capreomycin).
