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
Drugs in this class
- IsoniazidA first-line tuberculosis drug that blocks the bacillus's cell wall. Its key risks are hepatitis and peripheral…Enoyl-ACP reductase InhA (M. tuberculosis)
- RifampicinThe 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)
- PyrazinamideA 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
- EthambutolA first-line TB drug that protects the other drugs from resistance. Its hallmark risk is optic neuritis, with loss of…Arabinosyltransferase EmbB (M. tuberculosis)
- BedaquilineA 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)
- RifabutinA rifamycin that induces liver enzymes less than rifampicin, so it fits better with HIV protease inhibitors. It…DNA-dependent RNA polymerase, β subunit
- RifapentineA longer-acting rifamycin used in short preventive treatment with isoniazid and in a 4-month regimen for…DNA-dependent RNA polymerase, β subunit
- CycloserineAn 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
- EthionamideA 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)
- Aminosalicylic acidOne 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)
- DelamanidA nitroimidazole prodrug for drug-resistant TB, activated inside the bacillus. It is part of the 6-month BDLLfxC…Deazaflavin-dependent nitroreductase Ddn (activating enzyme)
- PretomanidA 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)
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.
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 (World Health Organization (WHO), 2025); Tuberculosis (World Health Organization (WHO), 2025); Tuberculosis (Ministerio de Salud y Protección Social de Colombia, 2024); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 65 (McGraw Hill, 2023).
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Representative model, for educational purposes only.