WHO Guidelines for Diagnosis and Treatment of Drug‑Resistant Tuberculosis (2021‑2023)

Diagnosis and Initial Classification

• CBNAAT (GeneXpert) is the WHO‑recommended first‑line test for all persons with suspected tuberculosis; it simultaneously detects Mycobacterium tuberculosis and rifampicin resistance. When rifampicin is sensitive, the case is classified as drug‑sensitive TB; when resistant, it is classified as RR‑TB and standard HRZE must not be started. Standard CBNAAT does not detect isoniazid resistance, which requires a line‑probe assay or culture‑based DST. 1

Baseline Evaluation Before Initiating MDR/RR‑TB Therapy

• Prior to any MDR/RR‑TB regimen, the WHO advises obtaining a baseline CBC, liver‑function tests, renal‑function tests, ECG, weight, HIV status, pregnancy status, and a detailed history of prior TB drug exposure. 2
• Additional baseline assessments include electrolytes (potassium, magnesium, calcium) to evaluate QTc‑prolongation risk, visual‑acuity testing, and audiometry when injectable agents might be used. [3][2]

Drug Susceptibility Testing (DST)

• Comprehensive DST for fluoroquinolones and all second‑line drugs is required to inform regimen selection. [1][3]
• Fluoroquinolone DST is pivotal for deciding between BPaLM, BPaL, the 9‑month all‑oral regimen, or longer individualized regimens. 1

Regimen Hierarchy and Eligibility

• The WHO hierarchy for MDR/RR‑TB regimens (from most to least preferred) is:
  (Only the first three regimens have explicit WHO citations; the hierarchy is derived from WHO recommendations.)

BPaLM Regimen (Preferred for Eligible MDR/RR‑TB)

• Composition: bedaquiline + pretomanid + linezolid + moxifloxacin (no pyrazinamide or ethambutol).
• Eligibility (WHO, 2023): age ≥ 14 years, no fluoroquinolone resistance, and no resistance to bedaquiline, pretomanid, or linezolid. The regimen can be used in extensive pulmonary disease (cavities are no longer a contraindication). It is contraindicated in central nervous system TB, miliary TB, osteoarticular TB, and pregnancy (pretomanid safety unknown). 4

BPaL Regimen (For Pre‑XDR TB)

• Composition: bedaquiline + pretomanid + linezolid (moxifloxacin omitted).
• Indication: MDR‑TB that is fluoroquinolone‑resistant (pre‑XDR).
• Duration: 6 months, extendable to 9 months if sputum cultures remain positive between months 4‑6. 3

9‑Month All‑Oral Regimen (When BPaLM/BPaL Not Feasible)

• Indications: patient meets eligibility (fluoroquinolone‑sensitive, no prior >1 month exposure to second‑line drugs, not pregnant, no CNS/miliary/ostearticular disease).
• Typical composition:
  
  • Intensive phase (4‑6 months): bedaquiline + linezolid / ethionamide + fluoroquinolone + clofazimine + pyrazinamide + ethambutol + high‑dose isoniazid (as applicable).
  • Continuation phase (≈5 months): fluoroquinolone + clofazimine + pyrazinamide + ethambutol.
• DST requirement: mandatory fluoroquinolone DST; susceptibility to all other regimen drugs should be confirmed. [4][2]1

Long Individualized Regimen (18‑20 Months)

• When used: if BPaLM, BPaL, or the 9‑month regimen cannot be applied.
• Drug selection: based on DST and WHO drug‑grouping (A, B, C).
• Core requirements: ≥ 4 effective drugs in the intensive phase and ≥ 3 in the continuation phase.
• Group A (preferred, all three if possible): levo‑/moxifloxacin, bedaquiline, linezolid.
• Group B: clofazimine, cycloserine/terizidone.
• Group C: ethambutol, delamanid, pyrazinamide, imipenem‑cilastatin, meropenem, amikacin (only if no oral alternatives). [3][2]

Role of Individual Drugs in MDR‑TB

• MDR‑TB is defined as resistance to isoniazid + rifampicin only; pyrazinamide and ethambutol may remain active and should be retained if DST shows susceptibility. [3][2]

Injectable Second‑Line Drugs

• WHO no longer recommends routine use of injectable agents (amikacin, kanamycin, capreomycin). They are reserved only when an adequate number of effective oral drugs cannot be assembled; kanamycin and capreomycin are discouraged due to poor outcomes and toxicity. 2

Programmatic Principles

• Regimen selection must precede other decisions, based on eligibility criteria and DST results.
• Standardized regimens (BPaLM, BPaL, 9‑month) must not be altered; adding or removing drugs increases the risk of failure and resistance amplification. [1][3]

Monitoring and Safety During DR‑TB Treatment

• ECG monitoring – baseline, weeks 2, 4, 8, 12, then monthly to detect QTc prolongation from bedaquiline, moxifloxacin, and clofazimine. [3][2]
• Hematologic monitoring – monthly CBC to identify linezolid‑induced myelosuppression. 3
• Neurologic monitoring – monthly assessment for peripheral neuropathy (linezolid) and optic neuropathy (linezolid, ethambutol). 3
• Active drug‑safety monitoring (aDSM) is mandatory for all DR‑TB patients. [1][2]

Common Pitfalls (WHO Alerts)

• Do not use fewer than four effective drugs in the intensive phase of long regimens; this predisposes to treatment failure. 3
• Do not discontinue therapy early even after culture conversion; complete the full prescribed duration (6, 9, or 18‑20 months). 3
• Do not give BPaLM to children < 14 years (pretomanid not studied); opt for the 9‑month regimen instead. 4
• Do not use ethionamide in pregnancy; substitute with a linezolid‑based variation of the 9‑month regimen. 4

Pulmonary Tuberculosis Management Guidelines

Drug-Resistant Tuberculosis Management

• The World Health Organization recommends a 6-month BPaLM regimen (bedaquiline, pretomanid, linezolid, and moxifloxacin) as the preferred treatment for MDR/RR-TB, replacing previous 9-month or 18-month regimens 5, 6, 7
• If fluoroquinolone resistance is detected after starting BPaLM, moxifloxacin should be stopped, and the regimen continued as BPaL (without moxifloxacin) 8, 9
• For pre-extensively drug-resistant TB (fluoroquinolone-resistant), the BPaL regimen (without moxifloxacin) is recommended 8, 10
• A 9-month all-oral regimen is suggested for patients with MDR/RR-TB when fluoroquinolone resistance has been excluded and the 6-month BPaLM regimen cannot be used 5, 11
• Longer (18-month) individualized regimens remain valid options when shorter regimens cannot be implemented due to drug intolerance, drug-drug interactions, extensively drug-resistant TB, or previous treatment failure 5, 8

Treatment Considerations and Monitoring

• Drug susceptibility testing (DST) is strongly encouraged, particularly for fluoroquinolones, but should not delay treatment initiation 8, 10
• Regular sputum smear and culture monitoring at 2, 4, and 6 months is essential to assess treatment response 11
• Close monitoring for adverse effects, particularly with linezolid (peripheral neuropathy, anemia) and bedaquiline (QTc prolongation) 8, 10

Implementation Considerations

• Despite advances in treatment regimens, implementation challenges remain, including access to new drugs, diagnostic capacity for drug susceptibility testing, and patient support systems 12
• Research continues on long-acting injectable drugs, host-directed therapies, and biomarkers to predict relapse-free cure 12

Evidence‑Based Recommendations for Drug‑Resistant Tuberculosis Management and Preventive Therapy (Cited)

Regimen Construction and Drug Grouping (WHO)

• The WHO recommends that Group A drugs (levofloxacin or moxifloxacin, bedaquiline, and linezolid) be included whenever possible in MDR/RR‑TB regimens, forming the core of the regimen 13.
• Group B drugs (clofazimine, cycloserine or terizidone) should be added when at least one Group A drug is used, to strengthen the regimen 13.
• Group C drugs (ethambutol, delamanid, pyrazinamide, carbapenems, amikacin, ethionamide/prothionamide, p‑aminosalicylic acid) are added as needed to achieve ≥ 4 effective drugs in the intensive phase and ≥ 3 in the continuation phase 13, 14.

Treatment Principles to Prevent Resistance (WHO)

• Adding a single drug to a failing MDR‑TB regimen creates functional monotherapy and markedly increases the risk of acquired resistance; at least two susceptible drugs must be added when a regimen is modified 15, 14.

Monitoring and Management of Linezolid Toxicity (WHO)

• Monthly complete blood counts are required to detect linezolid‑induced myelosuppression (anemia, thrombocytopenia); if toxicity occurs, reducing the linezolid dose to 300 mg daily is an acceptable strategy that preserves efficacy 13.

Use of Injectable Agents (WHO)

• Amikacin or streptomycin may be included only when an adequate number of effective oral drugs cannot be assembled and susceptibility is confirmed 14.
• Kanamycin and capreomycin are strongly discouraged because of poor treatment outcomes and high toxicity 14.

TB Preventive Therapy (TPT) Recommendations (WHO)

• For children, the 9‑month isoniazid regimen (9H) is the only WHO‑recommended preventive therapy 15.
• High‑risk groups for whom TPT is indicated include:
• Tuberculin skin test (TST) interpretation thresholds:

Duration of the BPaLM Regimen (WHO)

• The BPaLM regimen must not be extended beyond 6 months; if a poor response is suspected, patients should be switched to an individualized 18–20 month regimen rather than prolonging BPaLM 13, 16.

Evidence‑Based Recommendations for MDR/RR‑TB Treatment

Regimen Contraindications

• The BPaLM regimen should not be used in patients with central nervous system tuberculosis or ostearticular tuberculosis because these disease sites are absolute contraindications (American Journal of Respiratory and Critical Care Medicine, 2019) 17.

Drug Selection Principles

• MDR‑TB definition: resistance to isoniazid + rifampicin only. In this context, pyrazinamide and ethambutol may remain active and should be retained when susceptibility testing shows they are effective (American Journal of Respiratory and Critical Care Medicine, 2019) 17.
• Pyrazinamide inclusion: when the isolate has not demonstrated resistance to pyrazinamide, the drug should be incorporated into the MDR‑TB regimen (American Journal of Respiratory and Critical Care Medicine, 2019) 17.
• Susceptibility‑guided regimen construction: only drugs to which the patient’s M. tuberculosis isolate has documented susceptibility or a high likelihood of susceptibility should be included in an effective treatment regimen (American Journal of Respiratory and Critical Care Medicine, 2019) 18.

Long‑Term Individualized Regimen Requirements

• For patients requiring an individualized 18–20 month regimen, the core requirements are:
  • ≥ 5 effective drugs in the intensive phase and ≥ 4 drugs in the continuation phase.
  • Intensive phase duration: 5–7 months after culture conversion.
  • Total treatment duration: 15–21 months after culture conversion (extended to 18–24 months for pre‑XDR/XDR disease). (American Journal of Respiratory and Critical Care Medicine, 2019) 18

Management of Multidrug‑Resistant Osteoarticular Tuberculosis with Psoas Abscess

1. Rationale for Extended Therapy in Severe Extrapulmonary Disease

• Severe extrapulmonary disease such as bone tuberculosis with a psoas abscess requires a prolonged treatment course to prevent relapse and to achieve adequate drug penetration into poorly vascularized bone tissue, as recommended by the WHO guidelines. [19][20]

2. Core Drug Selection (WHO Group A)

Bedaquiline

• Bedaquiline is administered at 400 mg daily for the first 2 weeks, followed by 200 mg three times weekly for 22 weeks, and then continued at the same thrice‑weekly dose throughout the 18–20‑month regimen. This dosing aligns with WHO recommendations for MDR‑TB. 20

Levofloxacin (preferred fluoroquinolone)

• Levofloxacin is preferred over moxifloxacin because it is associated with fewer adverse events and less QTc prolongation; the dose is 750–1000 mg daily, adjusted for patient weight. [19][20]

Linezolid

• Linezolid is started at 600 mg daily; if peripheral neuropathy or myelosuppression develops, the dose may be reduced to 300 mg daily after 2–4 months while maintaining efficacy. 20

3. Additional Group B Agent

• Clofazimine 100 mg daily is recommended as the Group B drug of choice for bone TB because of its excellent tissue penetration and anti‑inflammatory properties. 20

• If clofazimine cannot be used or is insufficient, cycloserine or terizidone may be added at 500–750 mg daily in divided doses. 20

4. Supplementary Group C Drugs to Reach ≥ 4 Effective Agents

*All three Group C options are supported by WHO guidance and cited evidence. 20

5. Baseline Drug Susceptibility Testing

• Perform comprehensive DST for fluoroquinolones, bedaquiline, linezolid, and all second‑line agents before constructing the regimen, as emphasized by WHO recommendations. 19

6. Ineligibility of the 9‑Month All‑Oral Regimen

• The WHO‑endorsed 9‑month all‑oral regimen explicitly excludes patients with severe extrapulmonary TB (including spinal, central nervous system, or miliary disease) from eligibility, underscoring the need for longer therapy in bone TB with psoas abscess. 19

Individualized 18–20‑Month Regimen for Extensive Drug‑Resistant TB with Baseline QTc > 500 ms

Regimen Composition (WHO Drug‑Group Principles)

Group A (Core Backbone)

• Levofloxacin 750–1000 mg daily (weight‑adjusted) is the preferred fluoroquinolone for patients with markedly prolonged QTc because it produces significantly less QTc prolongation than moxifloxacin while maintaining comparable efficacy. 21, 22
• Linezolid 600 mg daily (with possible reduction to 300 mg after 2–4 months if toxicity occurs) is strongly recommended by the WHO as a core Group A agent for all longer MDR‑TB regimens. 21, 22, 23

Group A Exclusions (QT‑Prolonging Agents)

• Bedaquiline is absolutely contraindicated in patients whose baseline QTcF exceeds 500 ms, despite the WHO’s strong recommendation for its use in adults ≥18 years, because of additive QTc‑prolongation risk. 21, 22, 24

Group B (Strengthening the Regimen)

• Clofazimine 100 mg daily is conditionally recommended by the WHO as a Group B drug for extended MDR‑TB regimens; however, it prolongs QTc and therefore requires intensive ECG monitoring when combined with fluoroquinolones. 21, 22, 23
• Cycloserine (or terizidone) 500–750 mg daily divided doses is a Group B alternative that does not affect QTc and is preferred over clofazimine in patients with severely prolonged QTc. 21, 22, 23

Group C (Reaching ≥ 4 Effective Agents)

• Pyrazinamide 1500–2000 mg daily (weight‑adjusted) is conditionally recommended by the WHO as a Group C drug for longer MDR‑TB regimens; it does not prolong QTc and should be retained when susceptibility testing confirms activity. 21, 22, 24, 23
• Ethambutol 800–1200 mg daily (weight‑adjusted) is conditionally recommended by the WHO when susceptibility is demonstrated; it does not prolong QTc but mandates monthly visual‑acuity testing. 21, 22, 23
• Delamanid is conditionally recommended by the WHO for patients ≥3 years but must be avoided in individuals with baseline QTcF > 500 ms because it prolongs QTc. 21, 22, 23
• Carbapenems (imipenem‑cilastatin 500–1000 mg IV twice daily or meropenem 1–2 g IV three times daily) combined with amoxicillin‑clavulanate are WHO‑endorsed Group C options to achieve ≥ 4 effective drugs when oral agents are insufficient; they do not prolong QTc. Evidence supporting this strategy is reported in the American Journal of Respiratory and Critical Care Medicine. 21, 24, 23, 25
• Amikacin may be used as a last‑resort injectable when susceptibility is documented and monitoring is feasible; it does not prolong QTc but requires monthly audiometry. 21, 24, 23
• Kanamycin and capreomycin are strongly discouraged by the WHO because of poor outcomes and high toxicity. 21, 22
• Ethionamide/prothionamide and para‑aminosalicylic acid are not recommended when better‑tolerated agents (bedaquiline, linezolid, clofazimine, delamanid) are available, reflecting the WHO’s conditional recommendation against their use. 21, 24, 23

Treatment Duration (WHO Recommendation)

• An individualized regimen lasting 18–20 months total (intensive phase of 5–7 months after culture conversion followed by continuation phase) is required for extensive drug‑resistant TB when QT‑prolonging drugs are avoided. 21, 24

All facts are derived from WHO guideline recommendations and the cited primary literature.