The drug isoniazid is one of the most important tuberculosis drugs in standard therapy, which consists of rifampicin, isoniazid, pyrazinamide and ethambutol.

Isoniazid is administered over the entire 6-month duration of standard therapy. The dosage depends on body weight. If possible, it should be taken together with the other medications at least 30 minutes before breakfast, as this is the most effective way. If this makes it too difficult to tolerate, it can also be taken after a light breakfast or in the evening.

A possible side effect is an allergic reaction with skin rash and itching. The medication can damage the liver, so blood values must be checked at regular intervals. Alcohol should be avoided for the duration of the therapy in order not to put unnecessary additional strain on the liver. Nerve disorders can also occur, which are associated with numbness or tingling. Isoniazid can therefore be combined with vitamin B6 if nerve disorders are already known. Rarely does taking isoniazid have a negative effect on mood.

The treating physicians should be informed of any side effects so that they can react to them and possibly adjust the therapy.

If a medication in the standard therapy does not work or is intolerable, the composition and duration of the therapy can be changed. If the tablets are not taken regularly, the therapy may fail. The bacteria then begin to multiply again and can become resistant to the medication taken. This can lead to more complicated and longer treatment with poorer chances of recovery.