Toxicology – Carbamazepine Toxicity

Source

Carbamazepine is an anticonvulsant used for seizure disorders, trigeminal neuralgia, neuropathic pain, and bipolar disorder.

Typical Presentation

A patient, often after accidental or intentional ingestion, may develop marked drowsiness, unsteady gait, slurred speech, and altered mental status. Severe poisoning can progress to seizures, respiratory depression, coma, and cardiac conduction abnormalities.

Clinical Features

Possible findings include:

• Sedation and confusion
• Ataxia
• Dysarthria
• Nystagmus
• Anticholinergic features
• Respiratory depression
• Seizures
• Coma

ECG abnormalities may include:

• QRS widening
• QT prolongation
• Cardiac dysrhythmias in severe toxicity

Mechanism of Action

Carbamazepine blocks voltage-gated sodium channels, accounting for both its therapeutic anticonvulsant activity and many of its toxic effects. It is structurally related to tricyclic antidepressants and also has anticholinergic and sedating properties.

Management

Treatment is primarily supportive:

• Airway and respiratory support when needed
• Continuous cardiac monitoring and serial ECGs
• Benzodiazepines for seizures
• Sodium bicarbonate for clinically significant sodium-channel blockade with QRS widening
• Serial carbamazepine concentrations may be useful because absorption can be delayed and levels may continue to rise
• Multiple-dose activated charcoal may enhance elimination in selected significant poisonings
• Hemodialysis or hemoperfusion may be considered in severe or refractory toxicity with specialist guidance

Key Points

• Although carbamazepine treats seizures, overdose can itself cause seizures.
• Ataxia, nystagmus, sedation, and anticholinergic findings are common neurological clues.
• Sodium-channel blockade can produce dangerous cardiac conduction abnormalities.
• Chronic carbamazepine therapy may be associated with hyponatremia.