[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › Antituberculosis drugs [Pharmacology](https://durgical.com/en/pharmacology/) · Class # Antituberculosis drugs Medicines that kill or stop Mycobacterium tuberculosis. They are always combined so the bacillus cannot become resistant. Updated 2026-11-01 ## What they are The first-line drugs are isoniazid, rifampicin, pyrazinamide and ethambutol, which together cure most drug-susceptible tuberculosis in 6 months. Rifampicin-resistant or multidrug-resistant (MDR/RR) tuberculosis is treated with all-oral regimens built around bedaquiline, pretomanid or delamanid, linezolid, a fluoroquinolone and clofazimine; older second-line drugs (cycloserine, ethionamide, para-aminosalicylic acid) remain for when better options cannot be used. In Colombia the Ministry of Health buys these medicines centrally for its national TB programme. ## Mechanism of action Each drug hits a different part of the bacillus: rifamycins block bacterial RNA polymerase; isoniazid and ethionamide block mycolic acid synthesis (via the enzyme InhA); ethambutol blocks arabinogalactan assembly in the cell wall; pyrazinamide works in acidic sites inside macrophages and necrotic lesions; bedaquiline blocks the ATP synthase that powers the cell; delamanid and pretomanid are prodrugs activated inside the bacillus. Combining drugs with different targets means a bacillus would need several mutations at once to survive. Target: Several mycobacterial targets: RNA polymerase, mycolic acid and arabinogalactan synthesis, ATP synthase ## Key points - Never one drug alone: monotherapy selects resistant bacilli; first-line treatment is 2 months of isoniazid, rifampicin, pyrazinamide and ethambutol, then 4 months of isoniazid and rifampicin. - Isoniazid, rifampicin and pyrazinamide can all injure the liver; symptoms are asked about at every visit. - Isoniazid: peripheral neuropathy, prevented with pyridoxine (vitamin B6) in people at risk. - Rifampicin: orange-red urine, tears and sweat, and it lowers the levels of many drugs (HIV protease inhibitors, hormonal contraceptives, warfarin). - Ethambutol: optic neuritis (loss of acuity and of red-green colour vision); pyrazinamide: raised uric acid; bedaquiline: QT prolongation. ## Drugs in this class - [**Isoniazid** A first-line tuberculosis drug that blocks the bacillus's cell wall. Its key risks are hepatitis and peripheral… Enoyl-ACP reductase InhA (M. tuberculosis)](https://durgical.com/en/pharmacology/isoniazid/) - [**Rifampicin** The key sterilising drug for tuberculosis and leprosy. It turns urine and tears orange-red and speeds up the breakdown… DNA-dependent RNA polymerase, β subunit (M. tuberculosis)](https://durgical.com/en/pharmacology/rifampicin/) - [**Pyrazinamide** A first-line TB drug that works in acidic sites and allows treatment to last 6 months instead of 9. It raises uric… Aspartate decarboxylase PanD (M. tuberculosis), target of pyrazinoic acid](https://durgical.com/en/pharmacology/pyrazinamide/) - [**Ethambutol** A first-line TB drug that protects the other drugs from resistance. Its hallmark risk is optic neuritis, with loss of… Arabinosyltransferase EmbB (M. tuberculosis)](https://durgical.com/en/pharmacology/ethambutol/) - [**Bedaquiline** A key all-oral drug for drug-resistant tuberculosis that cuts off the bacillus's energy supply. Its main risk is QT… ATP synthase, subunit c (M. tuberculosis)](https://durgical.com/en/pharmacology/bedaquiline/) - [**Rifabutin** A rifamycin that induces liver enzymes less than rifampicin, so it fits better with HIV protease inhibitors. It… DNA-dependent RNA polymerase, β subunit](https://durgical.com/en/pharmacology/rifabutin/) - [**Rifapentine** A longer-acting rifamycin used in short preventive treatment with isoniazid and in a 4-month regimen for… DNA-dependent RNA polymerase, β subunit](https://durgical.com/en/pharmacology/rifapentine/) - [**Cycloserine** An older second-line TB drug that blocks D-alanine use in the cell wall. Its problem is the brain: depression… Alanine racemase and D-alanine–D-alanine ligase](https://durgical.com/en/pharmacology/cycloserine/) - [**Ethionamide** A second-line TB drug related to isoniazid that blocks the same enzyme, InhA. It is poorly tolerated: stomach upset… Enoyl-ACP reductase InhA (M. tuberculosis)](https://durgical.com/en/pharmacology/ethionamide/) - [**Aminosalicylic acid** One of the oldest TB drugs (PAS), a PABA look-alike that disrupts the bacillus's folate pathway. Stomach upset limits… Folate pathway of M. tuberculosis (acts downstream of dihydropteroate synthase)](https://durgical.com/en/pharmacology/aminosalicylic-acid/) - [**Delamanid** A nitroimidazole prodrug for drug-resistant TB, activated inside the bacillus. It is part of the 6-month BDLLfxC… Deazaflavin-dependent nitroreductase Ddn (activating enzyme)](https://durgical.com/en/pharmacology/delamanid/) - [**Pretomanid** A nitroimidazole prodrug for drug-resistant TB, the P in the 6-month BPaLM regimen. It kills both dividing and dormant… Deazaflavin-dependent nitroreductase Ddn (activating enzyme)](https://durgical.com/en/pharmacology/pretomanid/) ## Others in the class - Terizidone (a cycloserine analogue) - Protionamide (an ethionamide analogue) - Fixed-dose combinations of the first-line drugs - Amikacin and streptomycin (injectable aminoglycosides, only under strict conditions) ## Test yourself Think of the answer, then tap the question to see it. ## Why is tuberculosis always treated with several drugs at once? Because a large bacillary population always contains mutants resistant to any single drug; with several drugs of different targets, a bacillus would need several mutations at once. ## Which four drugs make up the intensive phase of drug-susceptible TB treatment? Isoniazid, rifampicin, pyrazinamide and ethambutol (HRZE). ## Which drug of the regimen is linked to colour vision loss? Ethambutol, through optic neuritis. ## What does BPaLM stand for? Bedaquiline, pretomanid, linezolid and moxifloxacin: a 6-month all-oral WHO regimen for MDR/RR-TB. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/classes/antituberculosis-drugs/) [← All of pharmacology](https://durgical.com/en/pharmacology/) Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given. Sources: [WHO consolidated guidelines on tuberculosis: module 4: treatment and care](https://www.who.int/publications/i/item/9789240107243) (World Health Organization (WHO), 2025); [Tuberculosis](https://www.who.int/news-room/fact-sheets/detail/tuberculosis) (World Health Organization (WHO), 2025); [Tuberculosis](https://www.minsalud.gov.co/salud/publica/PET/Paginas/Tuberculosis.aspx) (Ministerio de Salud y Protección Social de Colombia, 2024); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 65 (McGraw Hill, 2023). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/classes/antituberculosis-drugs/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/classes/antituberculosis-drugs/