A fixed-dose combination (FDC) of three first-line anti-tubercular drugs used primarily for the intensive phase of treatment for newly diagnosed pulmonary tuberculosis. Rifampicin is a bactericidal rifamycin, Isoniazid is a bactericidal isonicotinic acid hydrazide, and Ethambutol is a bacteriostatic synthetic compound. This combination is a cornerstone of the Revised National Tuberculosis Control Programme (RNTCP), now NTEP (National Tuberculosis Elimination Programme), in India to ensure adherence and prevent monotherapy.
Adult: ONE tablet (Rifampicin 450mg + Isoniazid 300mg + Ethambutol 800mg) once daily, taken on an empty stomach (1 hour before or 2 hours after food). This specific strength is for patients weighing 55kg and above. For patients 30-54kg, a lower strength FDC (e.g., Rifampicin 225mg + Isoniazid 150mg + Ethambutol 400mg) is used.
Note: Swallow whole with water. Take on an empty stomach for optimal absorption, especially of Rifampicin. If GI upset occurs, can take with a small amount of low-fat food, but consistency in timing is key. NEVER take with dairy products or antacids simultaneously (space by 2 hours).
Combined bactericidal and bacteriostatic action against actively dividing Mycobacterium tuberculosis. Rifampicin inhibits DNA-dependent RNA polymerase. Isoniazid inhibits mycolic acid synthesis. Ethambutol inhibits arabinosyl transferase, disrupting cell wall arabinogalactan synthesis.
Pregnancy: Pregnancy Category C (US FDA). All three drugs cross the placenta. TB treatment is essential in pregnancy. This regimen is used but requires careful monitoring. Pyridoxine supplementation (25-50 mg/day) is mandatory. Risk of neonatal bleeding due to Rifampicin; Vitamin K may be advised.
Driving: Caution advised. Visual disturbances (Ethambutol) and dizziness (CNS effects) may impair ability to drive or operate machinery.
| Warfarin | Rifampicin induces metabolism, drastically reducing anticoagulant effect. Increased warfarin dose needed; monitor INR closely. | Major |
| Oral Contraceptives | Rifampicin reduces efficacy, leading to contraceptive failure. Use non-hormonal backup. | Major |
| Antiretroviral Protease Inhibitors (e.g., Atazanavir, Darunavir) & NNRTIs (e.g., Efavirenz) | Rifampicin significantly reduces ARV levels, risking HIV treatment failure and resistance. Requires complex regimen adjustment. | Major |
| Ketoconazole/Itraconazole | Rifampicin reduces azole levels; azoles may increase Rifampicin toxicity. Avoid combination. | Major |
| Phenytoin, Carbamazepine | Rifampicin induces metabolism, reducing anticonvulsant levels. Isoniazid inhibits metabolism, increasing levels. Complex interaction; monitor levels. | Major |
| Corticosteroids (e.g., Prednisolone) | Rifampicin increases metabolism, reducing steroid efficacy. | Moderate |
| Antacids (Aluminum hydroxide) | Reduce absorption of Ethambutol and Isoniazid. Administer at least 2 hours apart. | Moderate |
| Acetaminophen (Paracetamol) | Increased risk of hepatotoxicity with Isoniazid. Use with caution. | Moderate |
| Pyridoxine (Vitamin B6) | Prevents/treats Isoniazid-induced peripheral neuropathy. Often co-prescribed. | Beneficial |
Same composition (Rifampicin (450mg) + Isoniazid (300mg) + Ethambutol (800mg)), different brands: