Drug-resistant tuberculosis is when not all drugs are effective against the tuberculosis bacteria.

If someone has tuberculosis, the tuberculosis bacteria are examined more closely in the laboratory. These tests, also known as susceptibility or resistance tests, are important in order to quickly determine the best possible therapy. Thanks to modern molecular genetic testing methods, the initial results of these tests are often available after just a few days. However, confirmation by longer-lasting culture procedures is still necessary.

Initially, the four standard drugs that are usually used for treatment are tested: Isoniazid, rifampicin, pyrazinamide and ethambutol. If a drug is not effective enough against the bacterium, this is referred to as resistance and the drug in question cannot be used. If there is resistance to rifampicin and isoniazid at the same time, this is referred to as multidrug-resistant (MDR) tuberculosis.

In the case of resistance, the treatment of tuberculosis is more difficult and sometimes takes longer, as the most effective standard therapy cannot be used. Medication must then be used that is less well tolerated and less effective. The chances of recovery are not as good as with drug-sensitive tuberculosis.

Resistance can develop if the medication is not taken in full, not taken for the recommended period or in the wrong dosage. However, direct infection with a resistant pathogen is also possible.