Drug resistance in tuberculosis

Multidrug regimens are necessary in all patients with TB to cover the possibility of pre-existing drug resistance and to prevent the emergence of resistant bacteria.

Isoniazid resistance is present in 10% of Mycobacterium tuberculosis isolates in Australia, predominantly in patients born overseas and in those who have previously been treated for TB. For patients with isoniazid-monoresistant TB, seek advice on treatment from the local TB authority—standard short-course therapy is not appropriate in these patients.

Note: Standard short-course therapy is not appropriate for patients with isoniazid-monoresistant TB.

Multidrug-resistant TB (MDR-TB), defined as TB resistant to at least isoniazid and rifampicin, is uncommon in Australia (about 1 to 3% of isolates) but is common in many other parts of the world. It should be suspected in:

people from countries with high rates of multidrug-resistant TB
patients in whom treatment has failed
patients who do not respond to treatment (either clinically or bacteriologically) within 3 months
contacts of patients with multidrug-resistant TB.

Rapid molecular testing (eg nucleic acid amplification testing [eg polymerase chain reaction (PCR)]) for rifampicin resistance is recommended if there is a risk of multidrug-resistant TB. If rifampicin resistance is detected, ensure that laboratory staff perform second-line drug susceptibility testing and, if indicated, rapid molecular testing for second-line drug resistance.

For more information about drug-resistant TB, see the World Health Organization website.