Rifampicin and Isoniazid is a combination of two highly effective anti-tuberculosis medicines. It belongs to the group of drugs known as antituberculosis agents and works by inhibiting the growth of Mycobacterium tuberculosis, the bacteria that cause tuberculosis. This combination is used during the continuation phase of tuberculosis treatment.

Rifampicin and isoniazid are bactericidal anti-tuberculosis drugs that are especially effective against rapidly growing extracellular mycobacteria and also show bactericidal activity against intracellular organisms. Rifampicin acts by inhibiting DNA-dependent RNA polymerase in susceptible bacterial cells. It specifically binds to bacterial RNA polymerase and does not inhibit the corresponding enzyme in mammalian cells. Cross-resistance to rifampicin has been observed only with other rifamycins. Rifampicin is also active against slowly growing and intermittently growing Mycobacterium tuberculosis. Isoniazid acts mainly against actively growing tubercle bacilli.

Body weight <50 kg: 3 tablet of 150/100 once daily or 1 tablet of 450/300 once daily

Body weight >50 kg: 2 tablet of 300/150 once daily

Hepatic impairment: Max: 8 mg/kg daily.

Rifampicin may reduce the effectiveness of hormonal contraceptives. Its absorption may also be reduced when taken with antacids.
Rifampicin can lower the plasma concentrations of several medicines, including certain antiviral drugs such as atazanavir, darunavir, and fosamprenavir, as well as atovaquone. It may also reduce serum levels of many other drugs, including anticonvulsants (such as phenytoin), antiarrhythmics (such as disopyramide), oral anticoagulants, antifungals (such as ketoconazole), barbiturates, beta-blockers, calcium channel blockers (such as diltiazem), chloramphenicol, clarithromycin, corticosteroids, ciclosporin, cardiac glycosides, clofibrate, dapsone, diazepam, doxycycline, fluoroquinolones (such as ciprofloxacin), haloperidol, oral hypoglycaemic agents (such as sulfonylureas), levothyroxine, methadone, narcotic analgesics, progestins, quinine, tacrolimus, theophylline, tricyclic antidepressants (such as amitriptyline and nortriptyline), and zidovudine. The risk of hepatotoxicity may be increased when rifampicin is used together with halothane.

Isoniazid may inhibit the metabolism of certain medicines, including anticonvulsants (such as carbamazepine and phenytoin), benzodiazepines (such as diazepam), haloperidol, ketoconazole, theophylline, and warfarin. Isoniazid may also enhance the central nervous system effects of meperidine, cycloserine, and disulfiram. In patients taking oral hypoglycaemic agents, isoniazid may interfere with blood glucose control.

Rifampicin and isoniazid is contraindicated in patients with known or suspected hypersensitivity to rifamycins, isoniazid (INH), or any of the excipients. It is also contraindicated in patients with a history of drug-induced hepatitis, acute liver disease of any cause, or peripheral neuritis.

Adverse effects may occur during continuous daily or intermittent therapy. Rifampicin may cause a reddish discoloration of body fluids and secretions, including urine, sputum, tears, faeces, saliva, and sweat. It may also permanently stain soft contact lenses.

Hepatic Effects: Very common (>10%) effects include asymptomatic elevation of liver enzymes. Severe hepatic reactions, such as hepatic failure and acute fulminant hepatitis, are uncommon (>0.1% and <1%). In rare cases (<0.01%), fatal outcomes have been reported.

Renal Effects: Increased levels of blood urea nitrogen (BUN) and serum uric acid, haemolysis, haematuria, interstitial nephritis, and renal insufficiency may occur.
Gastrointestinal Effects: Nausea, abdominal pain, vomiting, diarrhoea, and pseudomembranous colitis have been reported.

Central and Peripheral Nervous System Effects: Fatigue, drowsiness, headache, dizziness, ataxia, confusion, muscle weakness, and visual disturbances may occur.
Haematological Effects: Leukopenia, eosinophilia, thrombocytopenia, and thrombocytopenic purpura may be observed.

Skin and Appendage Effects: Flushing, itching with or without rash, urticaria, redness of the eyes, exudative conjunctivitis, and generalized hypersensitivity reactions involving the skin, such as exfoliative dermatitis, Lyell’s syndrome, and pemphigoid reactions, may occur.

Endocrine Effects: Disturbances in the menstrual cycle and precipitation of crises in patients with Addison’s disease may occur.

Adverse effects are more likely to occur during intermittent therapy or upon re-initiation of treatment after a temporary interruption.

This medicine is classified as Pregnancy Category C. Animal reproduction studies have shown adverse effects on the fetus, and there are no adequate and well-controlled studies in humans. However, the potential benefits may justify its use during pregnancy despite the possible risks.

The use of isoniazid should be carefully monitored in the following patients:

• Individuals who consume alcohol daily, as regular alcohol intake may increase the risk of isoniazid-induced hepatitis
• Patients with active chronic liver disease or severe renal dysfunction
• Patients older than 35 years of age
• Patients using any long-term concomitant medication
• Patients with a history of previous discontinuation of isoniazid
• Patients with peripheral neuropathy or conditions that may predispose them to neuropathy
• Pregnant women
• Individuals who use injectable drugs
• Women from minority groups, especially during the postpartum period
• HIV-seropositive patients

Combined anti-tubercular preparations

Store below 30°C, protected from light and moisture. Keep out of the reach of children.