Ethambutol / Isoniazid / Rifampicin

What it is and how it works

Rifampicin inhibits bacterial DNA-dependent RNA polymerase, isoniazid inhibits mycolic acid synthesis, and ethambutol inhibits arabinogalactan synthesis in the mycobacterial cell wall. Together they provide bactericidal activity against Mycobacterium tuberculosis while limiting the emergence of resistance.

Indications

Treatment of drug-susceptible tuberculosis in regimens that include ethambutol, isoniazid and rifampicin together, for example the continuation phase where national guidelines retain ethambutol or regimens in which pyrazinamide is omitted.

Dosage and administration (summary)

Oral, once daily on an empty stomach, number of tablets according to body-weight bands as specified for the tablet strength and by the national tuberculosis programme.

Contraindications

Hypersensitivity to any component, acute liver disease or severe hepatic impairment, jaundice, acute porphyria and pre-existing optic neuritis.

Warnings and precautions

Liver function should be monitored and treatment stopped if hepatitis develops; visual acuity and colour vision should be assessed because of the risk of ethambutol-induced optic neuritis. Pyridoxine is advised in patients at risk of isoniazid neuropathy, and rifampicin causes numerous enzyme-induction interactions and orange-red discolouration of body fluids.

Pregnancy

First-line antituberculosis drugs are considered appropriate in pregnancy, with pyridoxine supplementation.

Storage and supply

Store below 30 °C, protected from light and moisture.

Source: reference summary prepared from the EU SmPC/EPAR, BNF and WHO Model Formulary. The approved product information in Iran governs.