Drug resistance
Second-line drug
Agent usually reserved for the treatment of drug-resistant tuberculosis. First-line tuberculosis drugs used to treat drug-susceptible tuberculosis – ethambutol, isoniazid and pyrazinamide – may also be used in MDR-TB regimens.
Rifampicin-resistant tuberculosis (RR-TB)
Tuberculosis caused by a strain of M. tuberculosis complex that is resistant to rifampicin. These strains may be susceptible or resistant to isoniazid (i.e. MDR-TB), or resistant to other first-line or second-line tuberculosis drugs.
Primary drug resistance
Presence of drug resistance to one or more anti-tuberculosis drugs in a person who has received either no or less than one month of prior tuberculosis chemotherapy.
Polydrug resistance
Resistance to more than one first-line anti-tuberculosis drug (other than both isoniazid and rifampicin).
Pre-extensively drug resistant (XDR) tuberculosis
Tuberculosis caused by M. tuberculosis strains that fulfil the definition of multidrug-/rifampicin-resistant (MDR/RR-TB) and that are also resistant to any fluoroquinolone.
Multidrug- or rifampicin- resistant tuberculosis (MDR/RR-TB)
Refers to either multidrug-resistant tuberculosis (MDR-TB) or rifampicin-resistant tuberculosis (RR-TB). This term is used given that both drug resistance profiles are eligible for MDR-TB regimens.
Minimum inhibitory concentration (MIC)
The lowest concentration of an antimicrobial agent that prevents growth of more than 99% a microorganism in a solid medium or broth dilution susceptibility test.
Monoresistance
Resistance to only one first-line anti-tuberculosis drug.
High multidrug-resistant (MDR-TB) burden countries
20 countries with the highest estimated number of incident MDR-TB cases, plus the 10 countries with the highest estimated MDR-TB incidence that are not in the top 20 by absolute number (threshold: >1000 estimated incident MDR-TB cases per year).
Extensively drug-resistant tuberculosis (XDR-TB)
Tuberculosis caused by a strain of M. tuberculosis complex that is resistant to rifampicin (and may also be resistant to isoniazid), and that is also resistant to at least one fluoroquinolone (levofloxacin or moxifloxacin) and to at least one other “Group A” drug (bedaquiline or linezolid).
