Isoniazid / Rifampicin

What it is and how it works

Isoniazid inhibits synthesis of mycolic acids in the mycobacterial cell wall and is bactericidal against rapidly dividing Mycobacterium tuberculosis. Rifampicin inhibits bacterial DNA-dependent RNA polymerase and is bactericidal against both actively dividing and semi-dormant organisms.

Indications

Treatment of tuberculosis, usually in the continuation phase of standard regimens or with other agents in the initial phase; also used in some regimens for tuberculosis preventive therapy.

Dosage and administration (summary)

Given orally once daily on an empty stomach (at least 30 minutes before or 2 hours after a meal), with the number of tablets based on body weight to provide about rifampicin 10 mg/kg and isoniazid 5 mg/kg daily, according to national TB guidelines.

Contraindications

Hypersensitivity to either component; jaundice or active hepatic disease; previous isoniazid-associated hepatic injury; concomitant use with certain protease inhibitors (e.g. saquinavir/ritonavir).

Warnings and precautions

Hepatotoxicity may occur, especially in older patients, heavy alcohol users and those with chronic liver disease; monitor liver function and advise patients to report symptoms of hepatitis. Pyridoxine is recommended to prevent isoniazid peripheral neuropathy in at-risk patients. Rifampicin is a potent enzyme inducer that reduces the effect of many drugs (including hormonal contraceptives, warfarin, antiretrovirals, azoles and corticosteroids) and colours urine, tears and other body fluids orange-red.

Pregnancy

Standard first-line regimens are used in pregnancy; vitamin K is recommended for the mother and newborn when rifampicin is used in late pregnancy.

Storage and supply

Store below 25–30 °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.