Explain this TB regime
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WHO TB treatment regimen drug abbreviations HRZE MDR XDR 2023 2024
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TB Chemotherapy Regimens - Explained
The image shows a table titled "Composition of chemotherapy regimens" covering four categories of TB, each with an intensive phase and a continuation (maintenance) phase. Here is the full breakdown:
Drug Abbreviations Key
| Abbreviation | Drug |
|---|---|
| H | Isoniazid |
| R / Rb | Rifampicin / Rifabutin |
| Rpt | Rifapentine |
| Z | Pyrazinamide |
| E | Ethambutol |
| S | Streptomycin |
| Lfx | Levofloxacin |
| Mfx | Moxifloxacin |
| Sfx | Sparfloxacin |
| Bq | Bedaquiline |
| Lzd / Lzd(1,0) | Linezolid (1g then 0.6g) |
| Cs | Cycloserine |
| Trd | Terizidone |
| Dlm | Delamanid |
| Pto / Eto | Prothionamide / Ethionamide |
| Cm / Km / Am | Capreomycin / Kanamycin / Amikacin (injectables) |
| PAS | Para-aminosalicylic acid |
| Tpp | Thioacetazone + Pyrazinamide (or Thioacetazone alone, depending on context) |
| Imp/Mp | Imipenem/Meropenem |
| Pa | Pretomanid |
1. Drug-Sensitive TB (DS-TB)
Intensive phase (2-3 months):
H R/Rb Z E [S] - 4 drugs (the classic HRZE regimen). The handwritten annotation HRZE(s) confirms this. Streptomycin (S) is optional/bracketed.Continuation phase (4-12 months depending on disease pattern):
- Standard new case: 4 months HR or 4 months H R/Rpt Z (2-3 drugs)
- Relapse / previously treated (5+ months): 5 months H R/Rpt Z (3 drugs)
- Generalized TB + Meningitis (12 months): 12 months H R/Rb or 12 months H R/Rb Z (2-3 drugs)
- Other: 6 months H R/Rb/Rpt Z
The handwritten margin note shows: 3/3 → 4/12 (3 drugs intensive, 3 drugs continuation = total 4 months), and 5 → Relapse, and 12 → Generalized TB + Meningitis. The "3-2" margin note refers to 3 drugs intensive / 2 drugs continuation.
Rationale: The 4-drug intensive phase kills rapidly-dividing bacilli and prevents resistance emergence. HR in continuation mops up persisting organisms.
2. Isoniazid-Resistant TB
Intensive phase (3 months):
R/Rb Lfx/Sfx/Mfx [E] [Z] [Km/Am/Cm] [Pto/Eto] - 4 drugs. The handwritten annotation shows FRZE(K) - a fluoroquinolone (F) replaces isoniazid.Continuation phase (3-9 months): Same backbone:
R/Rb Lfx/Sfx/Mfx [E] [Z] [Km/Am/Cm] [Pto/Eto] - 4 drugs. Total duration therefore is 6-12 months.Rationale: Isoniazid is dropped since the organism is resistant to it. A fluoroquinolone (levofloxacin or moxifloxacin) substitutes to maintain bactericidal potency.
3. MDR-TB (Multidrug-Resistant TB)
MDR-TB = resistance to at least isoniazid + rifampicin.
Intensive phase (8 months):
Lfx/Mfx/Sfx Bq+ Lzd Cs/Trd + 1 drug [Dlm] [E] [Z] [Pto/Eto] [Cm/Km/Am] [PAS] [Tpp] - 5 drugs total. The handwritten annotation fLCsE(B) or BPaLN refers to combinations including bedaquiline, pretomanid, linezolid, and nitroimidazoles.Continuation phase (12-18 months):
Lfx/Mfx/Sfx Lzd [E] [Z] Cs/Trd [Pto/Eto] [PAS] [Tpp] - 3-4 drugs.The margin note shows 8 → 12/18 (intensive 8 months, continue to 12 or 18 months total), with a minimum of 6 months noted.
Rationale: MDR-TB requires longer, more complex regimens because first-line drugs are ineffective. Bedaquiline (ATP synthase inhibitor), linezolid (protein synthesis inhibitor), and fluoroquinolones form the new backbone of WHO-recommended all-oral MDR regimens. The BPaL/BPaLM regimen (Bedaquiline + Pretomanid + Linezolid ± Moxifloxacin) is now WHO-endorsed and can shorten treatment to 6 months in some patients.
4. Pre-XDR TB (Pre-extensively Drug-Resistant TB)
Pre-XDR = MDR-TB plus resistance to any fluoroquinolone.
Intensive phase (8 months):
Bq+ Lzd Lfx(1,0)/Mfx/Sfx Cs/Trd + 2 drugs [Dlm] [E] [Cm/Km/Am] [Z] [Imp/Mp] [Pto/Eto] [PAS] [Tpp] - 5 drugs. Note Lfx(1,0) means linezolid dosed at 1g then stepped down to 0.6g.Continuation phase (12-18 months):
Lzd Lfx(1,0)/Mfx Cs/Trd [E] [Z] [Pto/Eto] [PAS] [Tpp] - 3-4 drugs.Margin note: 8 → 12/19 (8 months intensive, 12-19 months total).
Rationale: Loss of fluoroquinolone efficacy forces reliance on repurposed drugs (imipenem/meropenem, delamanid, PAS). Injectable agents (Cm/Km/Am) are now largely discouraged due to toxicity; the trend is toward all-oral regimens.
5. XDR-TB (Extensively Drug-Resistant TB)
XDR = MDR-TB plus resistance to a fluoroquinolone and at least one injectable (or any additional agent per updated 2021 WHO definition).
Intensive phase (8 months):
Bq or Lzd Cs/Trd Dlm + 2 drugs [E] [Cm/Km/Am] [Z] [Imp/Mp] [Pto/Eto] [PAS] [Tpp] - 5 drugs. Note that bedaquiline or linezolid is listed (not both by default), reflecting the difficulty of constructing a regimen when most drugs have already failed.Continuation phase (12-18 months):
Cs/Trd + 2 drugs [Lzd] [E] [Z] [Pto/Eto] [PAS] [Tpp] - 3-4 drugs.Margin note: 8 → 12/18.
Rationale: XDR-TB has very limited drug options. BPaL (bedaquiline + pretomanid + linezolid) is a key salvage regimen. Surgery may be considered in localized disease.
General Principles Illustrated in the Table
- Two-phase approach: All regimens use an intensive phase (maximum drug killing) followed by a continuation/consolidation phase (eradication of persisting organisms).
- Brackets [ ] indicate drugs that are optional or chosen based on susceptibility testing and tolerability.
- Drug count: 4-5 drugs in the intensive phase; 3-4 in continuation.
- Duration scales with resistance: DS-TB: 6 months total; MDR/XDR: 20-26 months (or as short as 6 months with newer BPaL-based regimens).
- Trend toward all-oral regimens: Injectable aminoglycosides (Km, Am, Cm) are relegated to optional/bracketed roles, consistent with 2022 WHO guidelines.
The bottom of the image also mentions "Monitoring the effectiveness of treatment" - clinical monitoring is done daily in the intensive phase and at least monthly, consistent with WHO guidance. - Lippincott Illustrated Reviews: Pharmacology
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