Multidrug-resistant (MDR) TB is defined by resistance to at least isoniazid and rifampicin

Multidrug-resistant (MDR) TB is defined by resistance to at least isoniazid and rifampicin.

Extensively drug-resistant (XDR) TB is MDR plus resistance to a fluoroquinolone (eg moxifloxacin, ciprofloxacin) and one of three injectable agents
(kanamycin, capreomycin, amikacin).

Drug-resistant TB occurs if treatment has been wrongly prescribed, intermittent or incomplete, with the strongest risk factor being previous TB treatment.