What this test measures
This test determines whether a cultured M. tuberculosis isolate is sensitive or resistant to linezolid at the WHO-defined critical concentration. Linezolid is an oxazolidinone antibiotic that inhibits bacterial protein synthesis. It is one of the most important new drugs in TB and is part of the BPaL and BPaLM regimens for MDR / XDR TB.
Resistance is mediated by mutations in 23S rRNA (rrl) and rplC genes. Although still relatively uncommon, linezolid resistance is rising in patients exposed to long courses, which makes monitoring essential.
Why it matters
Linezolid has transformed XDR-TB outcomes. The 6-month BPaLM (Bedaquiline + Pretomanid + Linezolid + Moxifloxacin) regimen replaces the historical 18–24 month MDR-TB regimens with comparable or better cure rates. NTEP has been progressively rolling out BPaLM across India.
Confirming linezolid susceptibility before starting these regimens is essential. The drug has dose- and duration-dependent toxicities (anaemia, thrombocytopenia, peripheral and optic neuropathy) which require monitoring with blood counts and neurological assessment. Documented resistance changes regimen choice substantially.
How to prepare
A positive M. tuberculosis culture (MGIT or LJ) is required. If not available, sputum samples must be collected for AFB culture first.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
Modern all-oral TB regimens that depend on linezolid
| Regimen | Drugs | Duration |
|---|---|---|
| BPaL | Bedaquiline, Pretomanid, Linezolid | 6 months |
| BPaLM | Bedaquiline, Pretomanid, Linezolid, Moxifloxacin | 6 months |
| Longer MDR (NTEP) | Bdq, Lzd, Cfz, Cs, Lfx + others | 18–20 months |
Frequently asked questions
Why is linezolid so important in TB now?
Linezolid is the third pillar (with bedaquiline and pretomanid) of the 6-month BPaL/BPaLM regimens that have dramatically improved MDR/XDR-TB outcomes.
What side effects does linezolid cause?
Bone marrow suppression (anaemia, thrombocytopenia), peripheral neuropathy (numbness, tingling), optic neuropathy (vision change), and lactic acidosis. Side effects are dose- and duration-dependent — most regimens reduce the linezolid dose after the first 2 months.
How is linezolid monitoring done?
Regular CBC for anaemia and thrombocytopenia, clinical assessment for peripheral and optic neuropathy, and patient education to report visual or sensory symptoms early.
How long does the test take?
About 1–2 weeks from a positive culture; 4–6 weeks total from sputum collection.
Is linezolid available under NTEP?
Yes — NTEP supplies linezolid as part of MDR/XDR-TB regimens. Linezolid DST is offered at intermediate and national reference labs.
Can the linezolid dose be reduced if I develop side effects?
Yes — dose reduction (typically from 600 mg to 300 mg daily) is a standard strategy if toxicity develops, often without losing efficacy.
Is linezolid used outside TB?
Yes — for serious infections caused by gram-positive bacteria, particularly MRSA and VRE. TB use is at much longer duration, which is why monitoring is more intensive.
Related Tuberculosis / Mycobacterial tests
Tests commonly ordered alongside ANTIBIOGRAM - MTB (LINEZOLID), or that help interpret an unexpected result.
Sources & references
- WHO Consolidated Guidelines on Drug-Resistant TB · accessed 2026-05-30T00:00:00.000Z
- NTEP PMDT Guidelines · accessed 2026-05-30T00:00:00.000Z
- India TB Report 2024 · accessed 2026-05-30T00:00:00.000Z
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