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Antidote / Metabolic Agent Pregnancy: B - considered safe; L-carnitine is endogenous; use if benefit outweighs risk

L-Carnitine

Brand names: Carnitor, Levocarnil

Adult dose

Dose: Valproate toxicity / hyperammonaemia: 100 mg/kg IV loading (max 6 g), then 50 mg/kg IV every 8 h (max 3 g/dose). Oral maintenance: 1-3 g/day in divided doses
Route: IV / PO
Frequency: IV: 8-hourly until ammonia normalises and clinical improvement. PO: twice or three times daily
For valproate-induced hyperammonaemia (with or without hepatotoxicity): give IV. For chronic valproate therapy in at-risk patients (polypharmacy, malnourished, mitochondrial disease): consider PO supplementation.

Paediatric dose

Dose: 100 mg/kg
Route: IV
Frequency: Loading dose, then 50 mg/kg every 8 h
Max: 6000 mg loading dose; 3000 mg per subsequent dose
Infuse loading dose over 2-3 min IV. For primary carnitine deficiency in neonates/infants: 100-400 mg/kg/day IV or PO in divided doses - specialist metabolic guidance.

Dose adjustments

Renal

Use with caution in severe renal failure - secondary carnitine deficiency occurs in dialysis patients (standard supplementation 10-20 mg/kg IV post-dialysis).

Paediatric weight-based calculator

Infuse loading dose over 2-3 min IV. For primary carnitine deficiency in neonates/infants: 100-400 mg/kg/day IV or PO in divided doses - specialist metabolic guidance.

Clinical pearls

  • Valproate-induced hyperammonaemia can occur without hepatotoxicity - suspect if altered consciousness or encephalopathy in any patient on valproate.
  • Mechanism: valproate inhibits mitochondrial beta-oxidation of fatty acids, depletes carnitine, and impairs urea cycle - ammonia accumulates.
  • Also indicated for: primary carnitine deficiency (genetic), end-stage renal disease (dialysis-associated deficiency), and certain organic acidaemias (specialist use).
  • IV route preferred for acute toxicity - absorption from PO route is slower and unpredictable in encephalopathic patients.
  • Consider empirical L-carnitine in any patient on valproate with unexplained encephalopathy - safe and effective.

Contraindications

  • Known hypersensitivity to carnitine
  • Use caution in seizure disorder - rare reports of increased seizure frequency at high doses

Side effects

  • Nausea, vomiting, diarrhoea (PO route)
  • Fishy body odour (due to trimethylamine metabolite, PO)
  • Seizures (rare, high dose)
  • Muscle weakness at very high doses

Interactions

  • Valproate: valproate inhibits carnitine uptake and renal reabsorption - explains mechanism of deficiency
  • Pivampicillin / pivmecillinam (antibiotic prodrugs): deplete carnitine - avoid combination or supplement

Monitoring

  • Serum ammonia
  • Valproate level
  • LFTs (ALT, AST, bilirubin)
  • Prothrombin time / INR
  • Neurological status
  • Blood glucose

Reference: BNFc; TOXBASE; BNF 84; SPC Carnitor; AASLD Valproate Hepatotoxicity Guidance; Neurology Toolbox UK. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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