Antimicrobial resistance develops when treatment regimens are not properly administered or adhered to. It can also occur as a result of biological variations in drug uptake or substandard drugs. Multidrug-resistant (MDR) tuberculosis (TB) entails resistance to at least two of the most effective TB drugs, isoniazid and rifampicin. Extensively drug-resistant (XDR) TB includes additional resistance to any fluoroquinolone, and to any of the second-line injectable TB drugs (amikacin, capreomycin and kanamycin). Treatment of MDR TB lasts at least nine months. The shortest treatment regimen includes seven drugs taken for several months, involving a significantly higher risk for adverse drug effects. Costs of treatment for MDR and XDR TB are much higher than costs of treatment for drug-susceptible TB.