Drug-induced liver injury

DILI Basics - The Liver's Drug Problem

• A diagnosis of exclusion in acute liver injury of unknown cause.
• Two main types:
  • Intrinsic (Predictable): Dose-dependent, short latency (e.g., Acetaminophen toxicity via NAPQI metabolite).
  • Idiosyncratic (Unpredictable): Not dose-related, variable latency. Most common form (e.g., Augmentin, Isoniazid).
• 📌 Common Culprits: Antibiotics, Anticonvulsants, Acetaminophen, Allopurinol.

⭐ Hy's Law: Predicts severe DILI. Defined by hepatocellular injury (↑ ALT/AST >3x ULN) with ↑ Total Bilirubin >2x ULN, without cholestasis. Carries a 10-50% mortality risk.

Injury Patterns - A Tale of Two Cells

• Hepatocellular: Direct hepatocyte damage.
  • Labs: Predominant ↑↑ ALT.
  • Drugs: Acetaminophen, Isoniazid, Statins, Valproate.
• Cholestatic: Bile flow obstruction.
  • Labs: Predominant ↑↑ ALP.
  • Drugs: Augmentin, Anabolic steroids, OCPs.
• Mixed: Features of both.

Classification uses the R-value: $R = (ALT / ULN) / (ALP / ULN)$

• Hepatocellular: R ≥ 5
• Cholestatic: R ≤ 2
• Mixed: 2 < R < 5

⭐ Hy's Law: DILI causing hepatocellular jaundice (↑ Bilirubin) without initial cholestasis (normal ALP) indicates severe injury with >10% mortality risk.

The Detective Work - Diagnosis & Causality

• A diagnosis of exclusion requiring high suspicion and a meticulous drug/herb history (timing, dose, duration).
• Primary task: Rule out other causes (viral, autoimmune, alcoholic, metabolic, biliary obstruction).
• Calculate the R-value to classify injury pattern:
  • $R = (ALT_{patient} / ALT_{ULN}) / (ALP_{patient} / ALP_{ULN})$
  • Hepatocellular: R ≥ 5
  • Cholestatic: R ≤ 2
  • Mixed: 2 < R < 5
• Causality: Formally assessed with the Roussel Uclaf Causality Assessment Method (RUCAM).

⭐ Acetaminophen is the leading cause of drug-induced acute liver failure in the United States.

The Perp Lineup - Common Culprit Drugs

• Hepatocellular Necrosis (Direct & Idiosyncratic):
  • Acetaminophen (dose-dependent), NSAIDs, Statins
  • Isoniazid, Halothane, Valproate, Phenytoin
• Cholestatic Injury:
  • Amoxicillin-clavulanate, Erythromycin
  • Anabolic steroids, Oral contraceptives
• Other Patterns:
  • Amiodarone, Methotrexate (steatohepatitis, fibrosis)

📌 Mnemonic "Rule of A's": Acetaminophen, Augmentin, Allopurinol, Anesthetics (Halothane), Amiodarone, Antiepileptics.

⭐ Amoxicillin-clavulanate is a classic cause of cholestatic DILI, which can have a delayed onset of weeks to months, even after discontinuing the drug.

Damage Control - Management & Prognosis

• Primary Therapy: Prompt withdrawal of the suspected offending drug is critical.
• Management Algorithm:

⭐ Hy's Law: Key prognostic indicator. Defined as hepatocellular injury (↑ALT/AST >3x ULN) with ↑Total Bilirubin >2x ULN, portending a 10-50% mortality risk.

• Drug-Induced Liver Injury (DILI) is a diagnosis of exclusion after ruling out other common causes of liver disease.
• Acetaminophen toxicity is the leading cause of acute liver failure in the U.S.; the antidote is N-acetylcysteine.
• Intrinsic DILI is predictable and dose-dependent (e.g., acetaminophen), whereas idiosyncratic DILI is unpredictable.
• Key culprits include amoxicillin-clavulanate, isoniazid, anticonvulsants (valproate, phenytoin), and statins.
• The cornerstone of management is prompt withdrawal of the offending drug.