Multidrug-resistant and extensively drug-resistant tuberculosis.

Tuberculosis (TB) can usually be treated with a course of four standard, or first-line, anti-TB drugs. If these are misused or mismanaged (that is, when drugs are taken in the wrong combination, are fewer than those prescribed, or are taken in insufficient doses or not at the proper time), multidrugresistant TB (MDR-TB) can develop. MDR-TB is a form of disease resistant to the most important anti-TB drugs, i.e. isoniazid and rifampicin. MDR-TB takes longer to treat with second-line drugs, which are more expensive and have more side-effects. If these drugs are also misused or mismanaged, extensively drug-resistant TB (XDR-TB) can develop. Because XDR-TB is resistant to firstand second-line drugs, treatment options are seriously limited and so are the chances of cure.