Rechallenge Protocol for Anti-TB Drugs

Immediate Management of Drug Reactions

• The American Thoracic Society recommends stopping rifampicin, isoniazid, and pyrazinamide immediately if ALT/AST rises ≥5 times the upper limit of normal, or ≥3 times the upper limit of normal with hepatitis symptoms 4
• Investigate non-drug causes including viral hepatitis (A, B, C, E), biliary tract disease, alcohol use, and other hepatotoxic medications before attributing hepatotoxicity to TB drugs 4
• Continue treatment with non-hepatotoxic drugs (ethambutol 15-20 mg/kg daily, streptomycin, fluoroquinolones) if the patient has infectious TB or is clinically unwell until liver function normalizes 1

Sequential Drug Reintroduction Protocol

• The American Thoracic Society recommends reintroducing drugs in the following sequence: isoniazid first, then rifampicin, then pyrazinamide last, as isoniazid alone causes hepatitis in nearly 0% of cases, while pyrazinamide has the highest hepatotoxic potential 2
• Start isoniazid at 50 mg/day and increase to 300 mg/day after 2-3 days if no reaction occurs 2
• Start rifampicin at 75 mg/day after 2-3 days of full-dose isoniazid without reaction 2
• Start pyrazinamide at 250 mg/day after rifampicin is successfully reintroduced 2

Monitoring During Reintroduction

• Check liver function tests (ALT, AST, bilirubin, alkaline phosphatase) daily during the reintroduction phase 3
• Stop the most recently added drug immediately if transaminases rise again or symptoms develop 2

Alternative Regimens When a Drug Must Be Permanently Excluded

• Treat with rifampicin and isoniazid for 9 months total, supplemented with ethambutol for the initial 2 months if pyrazinamide cannot be used 2
• Treat with rifampicin, ethambutol, and a fluoroquinolone for at least 12 months if isoniazid cannot be used 3

Critical Risk Factors and Precautions

• Patients at highest risk for recurrent drug-induced liver injury include those with pre-existing liver disease or cirrhosis, chronic alcohol use, hepatitis B or C infection, HIV infection, malnutrition, advanced age (>35 years), and low pretreatment serum albumin 3
• Avoid concurrent use of other hepatotoxic medications (acetaminophen, alcohol, lipid-lowering agents) during TB treatment 4

When to Seek Expert Consultation

• Consult TB experts for complicated cases including multiple drug intolerances, drug-resistant TB, or when treatment options are extremely limited 6

Common Pitfalls to Avoid

• Never add a single drug to a failing regimen, as this creates de facto monotherapy and risks developing resistance to the new drug 7