MedCompanion

Latent Tuberculosis Infection

Mycobacterial

Source: IDMP View on spectrum chart →
Patient + scenario modifiers
Patient
Clinical scenario / source

Annotations only — chart still shows the full chemistry of each drug.

1. Clinical Syndrome

Positive immunologic evidence of TB exposure (IGRA — QuantiFERON, T-SPOT; or TST induration meeting cutoffs) without active disease — normal symptoms, normal CXR, negative sputum / no clinical findings. ~5–10% lifetime reactivation risk; higher in HIV / immunocompromised / recent converters / young children.

Excludes: active TB (separate syndrome — must rule out before LTBI tx with CXR + symptoms ± sputum), prior fully-treated TB (no further LTBI tx).

2. Pathogens

Consider the patient: Recent contact (high-risk converters), immunocompromise (HIV CD4, transplant candidate, biologics — anti-TNF, JAK inhibitors — drive screening + treatment), country of origin (high-incidence regions), age (children <5 + recent immigrants benefit most from treatment), pregnancy (often defer to postpartum unless recent conversion / HIV).

Consider the case: IGRA vs TST interpretation (IGRA not affected by BCG); recent conversion (within 2 years — highest reactivation risk); planned immunosuppression (treat LTBI before).

Common

    • Mycobacterium tuberculosis

      Dormant infection — no replication, no symptoms, no transmission. Treatment kills slow-growing bacilli before reactivation.

3. Empiric Therapy

TierFirst choiceAlternativesDurationComments
Outpatient
  • Weight-based (900 mg ≥50 kg) · PO weekly × 12 weeks · PO
  • 15 mg/kg (max 900 mg) + pyridoxine 25–50 mg · PO weekly × 12 weeks · PO
  • 10 mg/kg (max 600 mg) · PO daily × 4 months · PO

    **4R regimen.** Shorter than 9H + better completion. Drug interactions still apply.

  • 5 mg/kg (max 300 mg) + pyridoxine 25–50 mg · PO daily × 9 months · PO

    **9H regimen** — historic standard; longer + worse completion. Reserve for when 3HP / 4R contraindicated.

**3HP (preferred): 12 weeks. 4R: 4 months. 9H: 9 months. 1HP (HIV CD4 ≥100): 1 month.****3HP regimen (rifapentine + INH weekly × 12 wk)** is now CDC-preferred for most adults + children ≥2 yo. Better completion than 9H, shorter than 4R. **DOT not required** for 3HP in cooperative adults per 2018 CDC update; self-administered acceptable. **Always rule out active TB first** — CXR + symptom screen ± sputum (if symptomatic) before starting LTBI treatment (LTBI regimen would inadequately treat active disease + select resistance).

4. Directed Therapy

Pre-treatment workup:

  • IGRA (QuantiFERON, T-SPOT) preferred — unaffected by BCG; TST acceptable
  • CXR + symptom screen — must rule out active TB
  • HIV testing
  • LFTs baseline
  • Pregnancy test
  • Drug interaction review (esp rifamycins)

Regimen selection (CDC 2020):

  • 3HP (rifapentine + INH weekly × 12 weeks) — preferred for adults + children ≥2 yo
  • 4R (rifampin daily × 4 months) — preferred when rifapentine unavailable or interaction issue
  • 1HP (rifapentine + INH daily × 1 month) — for HIV+ adults/adolescents on compatible ART (WHO 2021)
  • 9H (INH daily × 9 months) — reserve when rifamycins contraindicated (drug interactions, intolerance)

Treat priority groups even with positive IGRA + no exposure: HIV+, transplant candidate, anti-TNF / JAK / B-cell-depleting candidate, silicosis, dialysis, recent converters (<2 years), close contacts of active TB, children <5 with positive test, foreign-born from high-incidence regions.

Adjuncts:

  • Pyridoxine 25–50 mg daily for all adults on INH
  • Monthly hepatic + clinical check-ins

Don't treat LTBI if: prior fully-treated TB, active TB suspected (rule out first), severe hepatic dysfunction (Child-Pugh C — risk-benefit), active alcohol abuse (defer).

5. Monitoring

Monthly clinical + symptom screen for hepatotoxicity + neuropathy. LFTs at baseline + as clinically indicated (more often if elderly, ETOH, baseline disease, HIV). Stop tx for AST/ALT >3× ULN with symptoms or >5× without.

Completion confirmation: no test of cure (IGRA / TST remain positive). Document completion to satisfy occupational health / pre-immunosuppression requirements.

Pearls

3HP is the modern preferred LTBI regimen — 12 doses weekly = best completion. Always rule out active TB first — LTBI regimens are inadequate for active disease + select resistance. Treat priority groups even without exposure: HIV+, transplant candidate, anti-TNF / biologics, recent converters. Pyridoxine with INH always. Pregnancy: defer to postpartum unless recent conversion. 4R (rifampin × 4 months) when rifapentine unavailable. HIV on ART: 1HP (1 month) per WHO 2021.

References