Isoniazid (INH) for Latent TB Infection

Decisions regarding INH treatment for latent TB Infection (LTBI) are balanced between:

  • 5% – 10% lifetime risk of Active TB
  • Higher risk with certain co-morbidities
  • Risk of INH-induced hepatitis (<0.4% at age 35; > 65 y.o. up to 4% risk)

In general, the younger the person, the less chance of hepatotoxicity, & the greater lifetime risk of active TB.  But some older persons carry great risks of Active TB.

Current CDC Guidelines from 2001 are somewhat vague.  Current interpretation of them  —  the following persons with LTBI should be treated:

1. Regardless of Age: persons with high risk of Active TB

• AIDS                        • HIV             • Silicosis
• Malnutrition              • Renal Failure (dialysis)
• Cancer:  head & neck, lymphoma, leukemia
• ChemoTx;  TNF-Inhibitors;  Organ Transplant Meds
• CXR w/ “old scars” of prior healed TB
• Infected (LTBI) within last 2 yrs (“conversion”)
 

2.  <65 y.o.:     • Diabetes     • Prednisone ≥15 mg/d for ≥1 mo

3.  <50 y.o.:     • Immigrants from high-prevalence countries in U.S. <5 yrs.
                        • Smokers         • Underweight persons w/ BMI <20
 

4.  <35 y.o.:     •  Everyone with Positive PPD/IGRA (regardless of time in U.S.)

Treatment Options

1.  INH 300 mg daily for 9 months (6 months acceptable)

2.  INH 900 mg + Rifapentine 900 mg once weekly
  • by directly observed therapy, x12 wks

3.  Rifampin 600 mg daily x4 mos [more side effects]

 Caveats
 
 Rx 30 days at a time; have pt seen q mo to review Sx of drug-induced hepatitis:
  • malaise, anorexia, nausea, upper abdominal pain
  • jaundice is pre-terminal (don’t emphasize this as Sx)
  • In case of Sx lasting >2 d, pt must a) d/c INH; AND b) come to clinic ASAP for LFTs
  • NOTE: purpose of review is so pt remembers danger signs during the following month
Pregnancy:  Usually begin INH 12 wks post-partum
  • incr. risk hepatitis earlier
  • Begin INH any time if pt at high risk of active TB
  • INH is not teratogenic [even in 1st trimester]

NEVER give INH for LTBI unless CXR normal (or work-up done for TB-4 [“old scar”; see posting TB-1 Intro]).

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