A 35-year-old man with focal seizures (temporal lobe epilepsy) has been on carbamazepine 600 mg/day for 3 years with good seizure control. He now presents with jaundice, dark urine, and abdominal discomfort. Liver function tests show: ALT 320 U/L, AST 280 U/L, bilirubin 4.2 mg/dL, ALP 95 U/L. Viral serology is negative. What is the most likely diagnosis and the immediate management?

Explanation

## Carbamazepine-Induced Hepatotoxicity **Key Point:** Carbamazepine causes idiosyncratic hepatotoxicity in 1 in 10,000–20,000 patients, presenting as acute hepatitis with jaundice, elevated transaminases, and systemic symptoms. Immediate discontinuation is mandatory to prevent fulminant hepatic failure. ### Clinical Features of Carbamazepine Hepatotoxicity | Feature | Presentation | |---------|-------------| | **Onset** | Usually within first 3 months; can occur later | | **Symptoms** | Jaundice, dark urine, abdominal pain, fever, rash (may precede hepatitis) | | **Biochemistry** | ↑ ALT/AST (hepatocellular pattern); mild ↑ ALP; ↑ bilirubin | | **Mechanism** | Idiosyncratic (not dose-related); likely metabolite-induced immune response | | **Severity** | Ranges from mild transient elevation to fulminant hepatic failure | | **Prognosis** | ~50% mortality if fulminant; recovery after discontinuation if caught early | **Clinical Pearl:** The patient's presentation (jaundice + dark urine + elevated transaminases with negative viral serology) is classic for idiosyncratic drug-induced hepatitis. The ALT/AST ratio and pattern (hepatocellular, not cholestatic) fit carbamazepine toxicity. **High-Yield:** Carbamazepine hepatotoxicity is an **idiosyncratic adverse effect** — it is NOT predictable from dose or serum levels and can occur even after years of stable therapy. Baseline LFTs should be checked before starting; routine monitoring during therapy does not reliably prevent severe cases but early recognition is critical. ### Management Algorithm ```mermaid flowchart TD A[Jaundice + ↑ transaminases on carbamazepine]:::outcome A --> B{Viral serology negative?}:::decision B -->|Yes| C[Suspect carbamazepine hepatotoxicity]:::outcome C --> D[Discontinue carbamazepine immediately]:::action D --> E[Check INR, bilirubin, albumin for severity]:::action E --> F{Fulminant hepatic failure?}:::decision F -->|Yes| G[ICU admission, consider transplant]:::urgent F -->|No| H[Supportive care, monitor LFTs daily]:::action H --> I[Switch to alternative AED after recovery]:::action I --> J[Avoid carbamazepine re-challenge]:::action ``` ### Alternative Antiepileptics After Carbamazepine Hepatotoxicity - **Levetiracetam:** minimal hepatic metabolism, no enzyme induction, safe choice - **Lamotrigine:** metabolized by glucuronidation, generally safe; avoid in severe hepatic impairment - **Oxcarbazepine:** structurally similar to carbamazepine; cross-reactivity risk (~25%), use with caution - **Valproate:** hepatotoxic risk; avoid - **Phenytoin:** hepatotoxic risk; avoid **Warning:** Do NOT continue carbamazepine while monitoring LFTs — this risks progression to fulminant hepatic failure. Do NOT re-challenge with carbamazepine; idiosyncratic reactions often recur with rechallenge.