Acute valproic acid overdose. Clinical course and pharmacokinetic disposition of valproic acid and metabolites.

Acute toxicity in the setting of valproic acid (valproate sodium) overdose is in most cases benign and readily reversible. However, serious toxicity has been reported. We present a case of accidental acute valproic acid overdose in a 26-month-old female, in whom serious neurological, metabolic, haematological and respiratory sequelae occurred. The major toxicity observed was delayed cerebral oedema. We also present data not previously reported, which describes the pharmacokinetic disposition of valproic acid and several of its metabolites during the course of this acute overdose. A comparison of an enzyme immunoassay and gas liquid chromatographic methodologies for measuring valproic acid in this setting is also presented. It appears that the 2-EN-valproic acid metabolite plays a role in the neurological toxicity.