How to Start Anti-Tuberculosis Therapy in Drug-Induced Liver Injury
If a patient develops drug-induced liver injury (DILI) during anti-tuberculosis treatment, immediately stop rifampicin, isoniazid, and pyrazinamide when AST/ALT rises to 5× normal or bilirubin rises, then bridge with streptomycin and ethambutol if the patient is unwell or smear-positive until liver function normalizes, followed by sequential drug reintroduction starting with isoniazid, then rifampicin, then pyrazinamide using graded challenge doses. 1
Initial Management: Stop Hepatotoxic Drugs
When AST/ALT reaches ≥5× upper limit of normal (ULN) or bilirubin rises, you must immediately discontinue all three hepatotoxic first-line drugs: rifampicin, isoniazid, and pyrazinamide 1.
Decision Point: Can You Wait or Must You Treat?
For non-infectious TB in stable patients: Hold all anti-TB drugs until liver function normalizes 1.
For infectious/severe TB (smear-positive or unwell patients): Continue treatment with streptomycin plus ethambutol as bridging therapy until liver enzymes normalize 1. This prevents disease progression and bacterial resistance while protecting the liver. Admit these patients for monitoring 1.
Sequential Drug Reintroduction Protocol
Once liver function returns to normal, reintroduce drugs one at a time in this specific order with daily clinical and biochemical monitoring 1:
Step 1: Isoniazid First
- Start isoniazid 50 mg/day
- After 2-3 days without reaction → increase to 300 mg/day
- Continue for another 2-3 days before adding next drug 1
Step 2: Add Rifampicin
- Start rifampicin 75 mg/day
- After 2-3 days without reaction → increase to 300 mg/day
- After another 2-3 days without reaction → increase to full dose:
- 450 mg if <50 kg
- 600 mg if >50 kg 1
Step 3: Add Pyrazinamide Last
- Start pyrazinamide 250 mg/day
- After 2-3 days without reaction → increase to 1.0 g/day
- Then increase to full dose:
- 1.5 g if <50 kg
- 2.0 g if >50 kg 1
If Rechallenge Fails
If hepatotoxicity recurs during reintroduction: Stop the offending drug permanently and use an alternative regimen 1.
If pyrazinamide is the culprit: Use rifampicin + isoniazid for 9 months total (instead of 6 months), with ethambutol for the first 2 months 1.
If multiple drugs cannot be reintroduced: Consider non-hepatotoxic regimens with ethambutol, fluoroquinolones, streptomycin, and cycloserine for 18-24 months under specialist supervision 1, 2.
Critical Monitoring Requirements
- Daily monitoring of clinical condition and liver function tests during each drug reintroduction phase 1
- Check for fever, malaise, vomiting, jaundice, or abdominal pain 1
- Measure ALT, AST, bilirubin, and alkaline phosphatase with each dose escalation 1
Important Caveats
Avoid fixed-dose combinations during rechallenge: You cannot identify the offending drug if using combination tablets 3. Use single-drug formulations for sequential reintroduction.
Consider NAT2 genotyping if available: Slow acetylators have higher isoniazid toxicity risk and may benefit from dose reduction 4, 5, 6. Recent evidence suggests phenotyping can guide safer isoniazid reintroduction in DILI patients 6.
Screen for viral hepatitis: Test for hepatitis B and C before restarting therapy, as coinfection increases DILI risk 1, 4.
Desensitization may be necessary: In drug-resistant TB where options are limited, formal desensitization protocols can be attempted under cover of two other effective anti-TB drugs to prevent resistance emergence 1.
Specialist consultation is mandatory when standard rechallenge fails or when designing alternative regimens 1.