Drug and Toxin Induced Liver Injury

DILI Classification & Intro - Liver's Drug Drama

• DILI: Drug-Induced Liver Injury; significant liver damage from medications, toxins, or herbals.
• Liver's Central Role: Primary site for drug metabolism, rendering it highly susceptible to injury.
• Major Classifications:
  • Intrinsic (Type A): 📌 Augmented pharmacological effect.
    • Predictable, strictly dose-dependent (e.g., Paracetamol).
    • Mechanism: Direct hepatotoxicity.
  • Idiosyncratic (Type B): 📌 Bizarre, unpredictable reactions.
    • Not dose-dependent; host genetic/immune factors critical.
    • Mechanisms: Immune-allergic, metabolic idiosyncrasy.
    • Examples: Halothane, Isoniazid, Phenytoin.
• Injury Patterns: Hepatocellular, cholestatic, or mixed.

⭐ Idiosyncratic DILI is unpredictable and not dose-dependent, unlike intrinsic DILI. vs Type B (Bizarre) Drug-Induced Liver Injury classification with examples of causative drugs for each type.)

Mechanisms of DILI - How Toxins Attack

• Direct Toxicity: Covalent binding of reactive drug metabolites (e.g., NAPQI from paracetamol).
• Immune-Mediated: Hapten formation, neoantigens trigger immune attack (e.g., halothane, phenytoin).
• Mitochondrial Dysfunction: ↓ATP synthesis, ↑ROS, leading to apoptosis/necrosis (e.g., valproate).
• Canalicular Injury/Cholestasis: Inhibition of bile salt export pumps (BSEP) (e.g., anabolic steroids, chlorpromazine).
• Steatosis/Steatohepatitis: Disrupted lipid metabolism, fat accumulation (e.g., amiodarone, methotrexate).
• Sinusoidal Endothelial Injury: Leads to SOS/VOD (e.g., cyclophosphamide).

⭐ Formation of reactive oxygen species (ROS) and subsequent oxidative stress is a common pathway in many types of DILI.

Key Drugs & Patterns - DILI Rogues' Gallery

• Hepatocellular Necrosis (predominant ↑ALT):
  • Paracetamol (Acetaminophen): Zone 3 (centrilobular) necrosis; predictable, dose-dependent.
  • Isoniazid (INH): Age-dependent risk, ↑ with Rifampicin; bridging necrosis.
  • Halothane: Immune-mediated "Halothane hepatitis"; potentially massive necrosis.
  • Ketoconazole, NSAIDs (e.g., Diclofenac): Idiosyncratic hepatocellular injury.
• Cholestatic/Mixed Injury (predominant ↑ALP/GGT or both ↑ALT & ↑ALP):
  • Amoxicillin-clavulanate: Commonest DILI; typically cholestatic or mixed.
  • Erythromycin, Chlorpromazine: Often bland cholestasis.
  • Oral Contraceptives/Anabolic Steroids: Cholestasis, hepatic adenoma, peliosis hepatis.
  • Sulphonamides, Phenytoin: Can cause mixed or cholestatic patterns.
• Steatosis & Fibrosis:
  • Valproic Acid: Microvesicular steatosis (Reye's-like syndrome), mitochondrial toxicity.
  • Amiodarone: Steatohepatitis (NAFLD-like), phospholipidosis; chronic use → fibrosis.
  • Methotrexate: Fibrosis/cirrhosis with chronic use, cumulative dose-related.
  • Tetracyclines (IV): Acute microvesicular steatosis.
• Autoimmune-like Hepatitis:
  • Methyldopa, Nitrofurantoin, Minocycline: Can induce autoimmune features (ANA/SMA+).
• Other Important Patterns/Drugs:
  • Statins: Generally safe; rare idiosyncratic DILI (hepatocellular/cholestatic).
  • Herbal & Dietary Supplements (HDS): Increasingly common; diverse patterns (Kava - hepatocellular).

⭐ Paracetamol overdose causes centrilobular necrosis (Zone 3); N-acetylcysteine (NAC) is the specific antidote.

DILI Diagnosis - Spotting the Suspect

Diagnosis involves careful drug history, excluding other causes, and assessing liver injury patterns.

⭐ The R-value (ALT/ULN ÷ ALP/ULN) helps classify DILI: >5 for hepatocellular, <2 for cholestatic, and 2-5 for mixed injury.

DILI Management - Damage Control Duty

• Stop Drug: Crucial first step. Discontinue suspected agent immediately.

  ⭐ The most crucial first step in managing suspected DILI is prompt withdrawal of the offending drug.

• Supportive Care: Maintain hydration, nutrition; manage any complications.
• Antidotes:
  • N-acetylcysteine (NAC) for paracetamol toxicity.
• Corticosteroids: Consider for DRESS or autoimmune features; benefit uncertain.
• UDCA: May be used for cholestatic DILI; evidence limited.
• Monitor: Serial LFTs to track liver injury progression/resolution.
• ALF: Liver transplantation for severe acute liver failure.
• Prevention: Strict avoidance of re-exposure; counsel patient.

High‑Yield Points - ⚡ Biggest Takeaways

• Paracetamol toxicity is dose-dependent, causing centrilobular necrosis via NAPQI; antidote is N-acetylcysteine.
• Aspirin in children with viral illness can cause Reye's syndrome with microvesicular steatosis.
• Isoniazid (INH) can induce acute hepatitis, especially with alcohol or advanced age.
• Methotrexate chronic use leads to hepatic fibrosis and cirrhosis.
• Halothane causes immune-mediated hepatitis with characteristic antibodies.
• Amiodarone toxicity can manifest as phospholipidosis or steatohepatitis.
• Oral contraceptives are linked to cholestasis and hepatic adenomas.