TB and Pre-existing Liver Disease — Complete MD Exam Answer (15 Marks)

INTRODUCTION

1. SPECTRUM OF PRE-EXISTING LIVER DISEASE IN TB PATIENTS

• Established chronic liver disease (cirrhosis, chronic hepatitis B or C, alcoholic liver disease, non-alcoholic fatty liver disease)
• Acute viral hepatitis (hepatitis A, B, C, E)
• Portal hypertension with ascites
• Hepatic TB itself — miliary TB involves the liver in ~30% of cases (granulomas detectable on serial sections); only 12% show granulomas on routine needle biopsy
• Drug-induced hepatitis from anti-TB drugs (DILI)

2. HEPATOTOXICITY OF ANTI-TB DRUGS

Isoniazid (INH)

• Most frequent cause of anti-TB drug-induced hepatitis
• Hepatotoxicity most frequent in adults >35 years, with daily alcohol use, malnutrition, diabetes, uraemia, and when other hepatotoxic drugs are co-administered
• Mechanism: toxic metabolite (acetylhydrazine) causes hepatocellular necrosis
• Isoniazid-induced hepatotoxicity is reversible if stopped early but can be fatal if continued
• Transient, asymptomatic rise in serum transaminases is common in early weeks — no need to interrupt treatment unless there is anorexia, malaise, vomiting, or jaundice

Rifampicin (RIF)

• Generally well tolerated at recommended doses
• Rarely causes serious hepatotoxicity (usually cholestatic pattern)
• Asymptomatic rises in serum transaminase are common and generally resolve spontaneously
• Accelerates hepatic cytochrome P450 pathway — reduces serum levels of many co-administered drugs
• Risk of adverse effects higher with intermittent regimens than daily regimens

Pyrazinamide (PZA)

• Rarely causes serious toxicity at currently recommended doses, but hepatotoxicity can occur at high dosages
• Severe hepatotoxicity has been specifically observed when rifampicin + pyrazinamide combinations are used (especially the 2-month R+Z regimen for latent TB)
• Pyrazinamide should NOT be used in patients with established chronic liver disease

Ethambutol & Streptomycin

• Non-hepatotoxic — these are the backbone of safe regimens in severe liver disease
• Ethambutol: main toxicity is retrobulbar neuritis (dose-dependent)
• Streptomycin: vestibular toxicity and ototoxicity; not for patients with renal disease

3. DRUG-INDUCED HEPATITIS (DILI) — MANAGEMENT

When to Stop Drugs

• Jaundice appears
• Anorexia, malaise, vomiting develop
• Mental changes (confusion, altered sensorium) — suggests impending acute liver failure
• Signs of bleeding — coagulopathy
• Protracted vomiting

Management Once Stopped

1. Stop all anti-TB drugs
2. Wait until jaundice resolves and liver enzymes return to baseline
3. If LFTs unavailable, wait 2 weeks after jaundice disappears
4. Seek other causes of hepatitis (viral hepatitis, drugs other than anti-TB)
5. During the waiting period, use non-hepatotoxic drugs — streptomycin + ethambutol ± fluoroquinolone — to prevent TB progression

Reintroduction of Anti-TB Drugs

• INH and rifampicin are least likely to cause reaction → reintroduced first
• Drugs more likely to cause reaction go last
• If initial reaction was severe, start with even smaller challenge doses
• If life-threatening hepatitis was not of viral origin, use the safer regimen of streptomycin + INH + ethambutol rather than re-introducing PZA

4. TREATMENT REGIMENS — PATIENTS WITH LIVER DISORDERS

(A) Established Chronic Liver Disease (e.g., cirrhosis, chronic hepatitis B/C)

• Pyrazinamide must be avoided — it is the most hepatotoxic
• Two recommended options:

• If there is ascites with portal hypertension (severe liver damage) — use only ONE hepatotoxic drug:

(B) Acute Viral Hepatitis Occurring During TB Treatment

• It is uncommon to have TB + acute viral hepatitis simultaneously
• But acute viral hepatitis during TB treatment is common (frequent cause of jaundice during TB treatment in many settings)
• Options:
  1. If TB disease is not severe → defer TB treatment until hepatitis resolves
  2. If TB must be continued → use streptomycin + ethambutol for maximum 3 months (safest interim regimen) → then switch to standard continuation phase: INH + RIF for 6 months (6HR)
  3. In extensive TB where more drugs are needed → a fluoroquinolone (e.g., ofloxacin) can be added to streptomycin + ethambutol as a non-hepatotoxic interim regimen

(C) Acute Liver Failure (Anti-TB DILI)

• Stop all hepatotoxic drugs immediately
• Bridge with non-hepatotoxic drugs: streptomycin + ethambutol ± fluoroquinolone
• Avoid ciprofloxacin (excreted by liver) — prefer ofloxacin or levofloxacin
• Restart cautiously once bilirubin normalises and LFTs return to baseline

5. MONITORING IN PATIENTS WITH PRE-EXISTING LIVER DISEASE

• Baseline LFTs mandatory before starting treatment
• Clinical monitoring at every visit: anorexia, nausea, vomiting, jaundice, abdominal pain, confusion
• Liver function tests (LFT): alanine aminotransferase (ALT), aspartate aminotransferase (AST), bilirubin — monitor at 2 weeks, 4 weeks, then monthly
• For patients with cirrhosis or portal hypertension → more frequent LFT monitoring
• Alcohol abstinence must be strictly advised (alcohol amplifies isoniazid hepatotoxicity)
• Avoid concomitant hepatotoxic drugs (e.g., azoles, statins, paracetamol in high doses)
• In HIV-TB co-infection with HBV/HCV co-infection and severe/chronic liver disease → start ART regardless of CD4 count (NACO guidelines)

6. TUBERCULOSIS OF THE LIVER (Hepatic TB)

• Granulomas found in 30% of TB cases on serial sections of liver biopsy
• Only 12% detected on routine needle biopsy (sampling error)
• Liver in TB shows:
  • Specific changes: necrotising lobular epithelioid cell granulomas (Figure 3.6, Sharma-Mohan) — large, confluent, caseating, with Langhans giant cells and lymphocyte cuffing
  • Non-specific changes: focal hyperplasia of Kupffer cells, non-specific reactive hepatitis
• Reticulin staining: poor reticulin fibres around and inside granuloma (helps differentiate TB from sarcoid — which has perigranuloma reticulin condensation)
• In miliary TB, liver biopsy demonstrating TB granulomas is valuable for diagnosis, especially in cryptic miliary TB with no miliary mottling on chest X-ray

7. SPECIAL SITUATIONS

Fluoroquinolones in Severe Liver Disease

• Fluoroquinolones (ofloxacin, levofloxacin) are useful when standard TB drugs are not tolerated, as in patients with severe liver disease
• Levofloxacin: more active and less toxic than ofloxacin, but more expensive
• Ciprofloxacin is excreted by the liver and should be avoided

TB in Patients with HIV + Chronic Liver Disease (HBV/HCV)

• NACO guidelines: start ART regardless of CD4 count if there is documented evidence of severe/chronic liver disease with HIV-HBV/HCV co-infection
• Overlapping hepatotoxicity between ARV drugs (NVP, EFV, NRTIs, PIs) and anti-TB drugs (INH, RIF, PZA) requires careful monitoring
• Preferred ART regimen: tenofovir + lamivudine + efavirenz (efavirenz has minimal drug-drug interaction with anti-TB drugs)

Alcoholism and Liver Disease

• Alcohol is an independent risk factor for TB (malnutrition, immunosuppression)
• Chronic alcohol use → predisposes to isoniazid hepatotoxicity
• Also a risk factor for TB-ARDS development
• Cycloserine must be avoided in patients with alcoholism (CNS toxicity)

SUMMARY TABLE: Regimen Selection Based on Severity of Liver Disease

KEY POINTS TO REMEMBER (for MD exam)

1. Pyrazinamide is the most problematic drug in liver disease — avoid in all grades of established chronic liver disease
2. Ethambutol and streptomycin are non-hepatotoxic — the safe backbone for alternative regimens
3. The more severe the liver disease, the fewer hepatotoxic drugs used and the longer the treatment duration (up to 12 months)
4. Jaundice, confusion, or bleeding = stop ALL anti-TB drugs immediately
5. Asymptomatic transaminase elevation alone is not an indication to stop treatment
6. After DILI resolves, INH and RIF are reintroduced first (least likely to cause reaction), PZA comes last
7. In severe liver disease, fluoroquinolones (ofloxacin, levofloxacin — NOT ciprofloxacin) provide useful non-hepatotoxic cover
8. Liver biopsy (demonstrating granulomas) is invaluable for diagnosing cryptic miliary TB in patients presenting with ARDS or unexplained hepatosplenomegaly