Toxicology – Valproic Acid (VPA) Toxicity

Source

Valproic acid is a prescription anticonvulsant also used for bipolar disorder and migraine prevention.

Typical Presentation

Following excessive valproic acid exposure, a patient may present with marked drowsiness, nausea, vomiting, and abdominal discomfort. Severe poisoning can progress to respiratory depression, coma, seizures, and cardiovascular instability.

Clinical Features

Toxicity is primarily neurological and gastrointestinal and may include:

• Nausea and vomiting
• Abdominal pain
• Confusion and lethargy
• Progressive CNS depression
• Seizures
• Coma
• Respiratory depression
• Hypotension

Important metabolic and organ complications include:

• Hyperammonemia
• Hepatic injury
• Pancreatitis
• Electrolyte abnormalities

Mechanism of Action

Valproic acid has several CNS effects, including enhancement of GABA activity and modulation of neuronal ion channels. In overdose, these actions contribute to significant CNS and respiratory depression.

Management

Treatment is primarily supportive:

• Airway and respiratory support when necessary
• Cardiac and neurological monitoring
• Serial valproic acid levels in significant toxicity
• Monitor ammonia, liver function, electrolytes, and acid-base status
• Gastrointestinal decontamination may be considered in selected recent exposures
• L-carnitine may be used in severe poisoning, particularly when hyperammonemia or significant hepatotoxicity is present
• Hemodialysis may be considered for life-threatening toxicity

Key Points

• Valproic acid toxicity can be delayed, particularly with extended-release preparations.
• Hyperammonemia is an important complication and may contribute to altered mental status.
• Severe toxicity can cause respiratory depression, hepatic dysfunction, cerebral edema, and shock.
• Serial drug concentrations may be necessary because levels can continue to rise after presentation.

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