title: Delayed valproic acid toxicity: a retrospective case series.
abstract: OBJECTIVE
  We estimate how often an initially undetectable or nontoxic valproic acid (VPA) concentration misrepresents the potential toxicity of an acute VPA overdose.
  
  
  METHODS
  All patients followed up by the San Diego and San Francisco Divisions of the California Poison Control System between January 1997 and June 1999 with a documented serum VPA concentration of 120 microg/mL or greater at any time were identified through a search of poison center databases. Cases involving patients who had serial VPA concentrations and an initial VPA concentration that was unmeasurable or less than 100 microg/mL were also identified. The methods of decontamination, clinical outcomes, highest measured concentration, and times after ingestion of the initial and highest measured concentration of VPA were determined by means of chart review for these cases.
  
  
  RESULTS
  Of the 173 patients identified with VPA concentrations of 120 microg/mL or greater, 21 (12.1%) had a detectable initial concentration not in the toxic range, and 5 (2.9%) had initial concentrations of less than the limit of detection. These 26 cases involved acute ingestion of VPA preparations. Four of these 26 patients were discharged to home or to a psychiatric facility after the initial results were obtained.
  
  
  CONCLUSIONS
  Delayed toxicity might occur in patients after an acute overdose of enteric-coated VPA. Initial serum VPA concentrations might be misleading. Serial measurements documenting declining VPA concentrations or prolonged observation are recommended to determine whether a patient is medically safe for discharge or psychiatric placement.
authors.affiliation: San Diego Division, California Poison Control System, San Diego, CA, USA.
authors.forename: Marianne
authors.initials: M
authors.lastname: Ingels
authors.forename: Jon
authors.initials: J
authors.lastname: Beauchamp
authors.forename: Richard F
authors.initials: RF
authors.lastname: Clark
authors.forename: Saralyn R
authors.initials: SR
authors.lastname: Williams
mesh_terms: D000293:Adolescent; D000328:Adult; D000927:Anticonvulsants / Q000097:blood / Q000506:poisoning*; D002140:California / Q000453:epidemiology; D002606:Charcoal / Q000627:therapeutic use; D002648:Child; D062787:Drug Overdose; D005751:Gastric Lavage; D006801:Humans; D008875:Middle Aged; D011039:Poison Control Centers / Q000706:statistics & numerical data; D012189:Retrospective Studies; D013997:Time Factors; D014635:Valproic Acid / Q000097:blood / Q000506:poisoning*
chemical_list: D000927:Anticonvulsants; D002606:Charcoal; D014635:Valproic Acid