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DRUG-SENSITIVE TB (DSTB) AND DRUG-RESISTANT TB (DRTB): COMPREHENSIVE ANSWER (15 Marks)

PART A: DRUG-SENSITIVE TUBERCULOSIS (DSTB)

Definition

Drug-sensitive TB (DSTB) is tuberculosis caused by Mycobacterium tuberculosis susceptible to first-line anti-TB drugs, particularly rifampicin and isoniazid.

Classification of Anti-TB Drugs

First-line drugs: Rifampicin (R), Isoniazid (H), Pyrazinamide (Z), Ethambutol (E), Streptomycin (S)

Second-line drugs: Fluoroquinolones (Levofloxacin, Moxifloxacin), injectable agents (Amikacin, Kanamycin), Bedaquiline, Linezolid, Cycloserine, Ethionamide, PAS, Delamanid (Sharma & Mohan, Ch. 44)

Standard Treatment Regimen for New DS-TB Patients

Phase	Drugs	Duration	Notes
Intensive Phase (IP)	HRZE	2 months	Kills actively growing & semi-dormant bacilli; 80–90% smear conversion
Continuation Phase (CP)	HR (+ E if H-resistance suspected)	4 months	Sterilising effect; eliminates residual bacilli

Recommended regimen: 2HRZE / 4HR (optimal) or 2HRZE / 4HRE (if H-resistance suspected) (Sharma & Mohan, Ch. 44; Table 44.6)

Drug Doses (Daily; adults)

Drug	Dose (mg/kg/day)	Maximum (mg)
Isoniazid (H)	5 (range 4–6)	300
Rifampicin (R)	10 (range 8–12)	600
Pyrazinamide (Z)	25 (range 20–30)	—
Ethambutol (E)	15 (range 15–20)	—
Streptomycin (S)	15 (range 12–18)	1000

(Sharma & Mohan, Table 44.7)

In TB meningitis: replace Ethambutol with Streptomycin.

Principles of Treatment

Regimens must contain a combination of drugs (to prevent emergence of resistance)
IP eliminates large rapidly-multiplying bacillary populations; prevents early death
CP targets semi-dormant persister organisms with sterilising drugs; prevents relapse
Thrice-weekly intermittent treatment has been discontinued; daily therapy is recommended
Universal DST is now mandatory before assigning treatment regimen
Treatment must be registered on Nikshay portal (PMDT 2021, Slide 48)

Follow-up in DS-TB

Sputum smear/culture at end of IP, and if positive during CP
If smear-positive during CP → send for rapid molecular DST / culture-DST for R and H resistance (Sharma & Mohan, Ch. 44)

PART B: DRUG-RESISTANT TUBERCULOSIS (DRTB)

Definitions and Classification (PMDT 2021, Slide 9)

Type	Definition
Mono-resistant TB (MR-TB)	Resistant to ONE first-line drug only
Isoniazid-resistant TB (Hr-TB)	Resistant to H; susceptible to R
Poly-drug resistant TB (PDR-TB)	Resistant to >1 first-line drug, but NOT both H and R
Rifampicin-resistant TB (RR-TB)	Resistant to R (with or without other resistance); detected phenotypically or genotypically
MDR-TB	Resistant to BOTH H and R (± other drugs)
Pre-XDR-TB	MDR/RR-TB + resistant to any fluoroquinolone
XDR-TB	MDR/RR-TB + resistant to any fluoroquinolone (Lfx or Mfx) + at least one Group A drug (Bdq or Lzd)

Causes of DR-TB (PMDT 2021, Slide 5)

Category	Examples
Microbial	Random chromosomal mutations (H resistant 1 in 10⁶; R resistant 1 in 10⁸; H+R 1 in 10¹⁴)
Programmatic	Inadequate supply/poor quality drugs, stock-outs, wrong combinations, inadequate training
Clinical	Non-compliance, poor adherence, adverse drug reactions, substance abuse, malabsorption, social barriers

Diagnosis of DR-TB

Methods of Drug Resistance Testing (DRT) and DST:

NAAT (CBNAAT/Truenat): Detects MTB + RR-TB simultaneously; point-of-care
Xpert MTB/XDR: Follow-on test; detects resistance to H, FQ, SLI and Eto
Line Probe Assay (LPA):
- FL-LPA: detects resistance to R, H (katG + inhA mutations)
- SL-LPA: detects resistance to FQ and SLI
Liquid Culture (MGIT 960): DST for first-line and second-line drugs; monitors treatment response (PMDT 2025, Slide 3)

Integrated Diagnostic Algorithm:

All presumptive TB → NAAT → if RR detected: FL-LPA + SL-LPA + LC-DST
If RR not detected: FL-LPA for H resistance
Results entered into Nikshay portal same day

Drug Grouping for DR-TB Treatment (PMDT 2021, Slide 36; WHO 2020)

Group	Drugs	Use
Group A	Levofloxacin/Moxifloxacin, Bedaquiline, Linezolid	Include ALL 3
Group B	Clofazimine, Cycloserine/Terizidone	Add 1 or both
Group C	E, Delamanid, Z, Imipenem-cilastatin/Meropenem, Amikacin, Eto/Pto, PAS	Add to complete regimen

Kanamycin and Capreomycin are no longer recommended (associated with poorer outcomes).

Treatment Regimens for DR-TB (PMDT 2025, Slides 7–27; PMDT 2021)

1. H Mono/Poly DR-TB Regimen

Regimen: Lfx + R + Z + E (6–9 months, no IP/CP separation)
Duration: Standard 6 months; extended to 9 months if: extensive disease, uncontrolled comorbidity, EP-TB, or smear positive at end of month 4
Replacement: If Lfx can't be used → Mfxh; if Z can't be used → Lzd; if both Mfx+Z can't be used → add 2 of: Lzd, Cfz, Cs

2. BPaLM Regimen (6–9 months) — Priority regimen for MDR/RR-TB (PMDT 2025)

Drugs and Doses:

Drug	First 2 weeks	Weeks 3–26/39
Bedaquiline (Bdq)	400 mg once daily	200 mg 3× per week
Pretomanid (Pa)	200 mg daily	200 mg daily
Linezolid (Lzd)	600 mg once daily	600 mg once daily
Moxifloxacin (Mfx)	400 mg once daily	400 mg once daily

Inclusion criteria (BPaLM):

Age ≥14 years
New microbiologically confirmed RR-TB
QTcF ≤450 ms (male), ≤470 ms (female)
No prior treatment with Bdq, Lzd, Pa for >1 month (unless sensitivity documented)

Exclusion criteria (BPaLM):

Age <14 years
Documented resistance to Bdq, Lzd or Pa
Significant liver dysfunction (LFT >3× ULN)
Severe EP-TB (CNS TB, spinal/skeletal, disseminated TB)
Pregnant or lactating women
Significant cardiac abnormalities / Long QT syndrome
Hb <8 g/dL (not rapidly correctable), severe neutropenia (<750/mm³) or thrombocytopenia (<100,000/mm³)

Pyridoxine supplementation (to prevent neuropathy):

Weight	Dose
16–29 kg	50 mg
30–45 kg	100 mg
46–70 kg	100 mg
>70 kg	100 mg

Linezolid dose reduction: If severe grade 3 toxicity occurs before 9 weeks → declare regimen failed; after 9 weeks → reduce to 300 mg (extends regimen to 39 weeks)

3. Shorter Oral MDR/RR-TB Regimen (9–11 months)

Preferred for children <14 years and when BPaLM not eligible.

Eligibility: RR-TB ± H resistance (katG or inhA, NOT both), FQ resistance not detected, no extensive disease, no severe EP-TB
Regimens (options):
- A: (2) Lzd + (4–6) Lfx + Cfz + Z + E + Hh / (6–9) Bdq + (5) Lfx + Cfz + Z + E
- B: (4–6) Lfx + Cfz + Eto + Z + E + Hh / (6–9) Bdq + (5) Lfx + Cfz + Z + E (if Lzd intolerant/resistant)

Exclusion: Bilateral cavitary disease, >3 zones with cavities, severe EP-TB (miliary/CNS/spinal), history >1 month use of Bdq/Lfx/Cfz/Eto, pregnant (>24 weeks), children <5 years

4. Longer Oral M/XDR-TB Regimen (18–20 months)

Individualized based on DST
Start with all 3 Group A agents + ≥1 Group B agent (minimum 4 effective drugs)
Continue with 4 drugs beyond 6–9 months; if only 1–2 Group A agents usable → both Group B agents must be included
Regimen: (6–9m) Bdq + (18–20m) Lfx + Lzd + Cfz + Cs

Pre-Treatment Evaluation (PTE) for DR-TB (PMDT 2025, Slide 10)

Clinical	Laboratory
History + physical examination	CBC (Hb, TLC, DLC, platelets)
Previous ATT (especially Bdq, Pa, Dlm, Lzd)	LFT + viral markers
BMI / nutritional status	Serum electrolytes (Na, K, Mg, Ca)
Neurological evaluation	Random blood sugar
Ophthalmic evaluation (visual acuity, colour vision)	Urine pregnancy test
—	HIV testing, ECG, Chest X-ray

Follow-Up Monitoring — BPaLM Regimen (PMDT 2025, Slides 15–16)

Assessment	Frequency
Clinical review + weight/BMI	Monthly
CBC + ECG	Day 15, 30, then monthly
Visual acuity + colour vision	Weeks 9, 13, 26
Sputum smear + culture	Monthly from month 2
DST (NAAT MTB/XDR or LPA + LC-DST)	If culture +ve at month 4, end of treatment
LFT + CXR	End of month 3, end of treatment
Long-term follow-up	At 6, 12, 18, 24 months post-treatment

Special Situations

Pregnancy and Lactation (PMDT 2025, Slides 19–20)

BPaLM is contraindicated in pregnancy/lactation
SLIs contraindicated (8th cranial nerve toxicity to foetus)
Eto contraindicated before 32 weeks (teratogenic)
Recommended: 9-month shorter oral MDR/RR-TB regimen with Lzd
If gestation >20 weeks and patient unwilling for MTP → 9-month shorter or longer oral regimen

Children (PMDT 2025, Slide 21)

BPaLM (with Pa): safety not established for <14 years
Children <14 years → 9–11 month shorter or 18–20 month longer oral regimen
Children <5 years: Bdq not available → replaced by Am/Km (shorter) or Dlm (longer)

PLHIV (PMDT 2025, Slide 22)

BPaLM can be given regardless of HIV status/CD4 count (if other criteria met)
Avoid Efavirenz (reduces Bdq and Pa exposure)
Use Dolutegravir (DTG) with BPaLM
Avoid Zidovudine with Lzd (myelosuppression cross-toxicity)

Treatment Outcomes (Definitions)

Cured: Smear/culture negative at end of treatment + at least one previous negative
Treatment Failed: Smear/culture positive at month 5 or later (or earlier decision based on clinical deterioration)
Lost to follow-up, Not evaluated, Treatment success as per standard definitions

Key Points to Remember

Universal DST must precede treatment assignment
All patients registered on Nikshay; never batch specimens — transport immediately
Supervised therapy (≥85% doses supervised) is critical for BPaLM
Monitoring turnaround time improves outcomes
Long-term follow-up for 2 years after completing any DR-TB regimen
Post-treatment 6-monthly follow-up must be performed strictly for 2 years in every DR-TB patient

Sources: Sharma SK & Mohan A – Textbook of Tuberculosis and NTM Diseases, 3rd Ed., Ch. 44 (Treatment of Tuberculosis); PMDT Guidelines India 2021 (NTEP); PMDT Guidelines India March 2025 (Updated National Guidelines on Management of Drug-Resistant TB)

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