The advent of
antibiotics for the treatment of
tuberculosis (TB) represented a major breakthrough in the fight against the disease. However, since its first use,
antibiotic therapy has been associated with the emergence of resistance to drugs. The incorrect use of anti-TB drugs, either due to prescription errors, low patient compliance, or poor quality of drugs, led to the widespread emergence of Mycobacterium tuberculosis strains with an expanding spectrum of resistance. The spread of multidrug-resistant (MDR) strains (ie, strains resistant to both
isoniazid and
rifampicin) has represented a major threat to TB control since the 1990s. In 2006, the first cases of MDR strains with further resistance to
fluoroquinolone and
injectable drugs were described and named extensively
drug-resistant TB (
XDR-TB). The emergence of
XDR-TB strains is a result of mismanagement of MDR cases, and treatment relies on drugs that are less potent and more toxic than those used to treat
drug-susceptible or MDR strains. Furthermore, treatment success is lower and mortality higher than achieved in MDR-TB cases, and the number of drugs necessary in the intensive phase of treatment may be higher than the four drugs recommended for MDR-TB.
Linezolid may represent a valuable
drug to treat cases of
XDR-TB.
Delamanid,
bedaquiline, and
PA-824 are new anti-TB agents in the development pipeline that have the potential to enhance the cure rate of
XDR-TB. The best measures to prevent new cases of
XDR-TB are the correct management of MDR-TB patients, early detection, and proper treatment of existing patients with
XDR-TB.