Delayed peak serum valproic acid in massive divalproex overdose--treatment with charcoal hemoperfusion

Increased clearance and apparent clinical improvement in valproic acid overdose has been reported following in-series hemodialysis/hemoperfusion therapy. We report a case of divalproex sodium and chlorpheniramine overdose treated with charcoal hemoperfusion and multiple-dose activated charcoal.

A 32-year-old female presented alert three hours postingestion of her own medication. Serum valproic acid was 105 micrograms/mL. No anticholinergic toxicity was seen. Despite three doses of activated charcoal over 14 hours, serum valproic acid continued to rise. Whole bowel irrigation and multiple-dose activated charcoal were commenced 17 h postingestion when serum valproic acid was 1380 micrograms/mL. Charcoal hemoperfusion was instituted three hours later when serum valproic acid had not fallen and the patient remained obtunded.

Initial extraction ratio of the hemoperfusion cartridge was 0.54 with plasma clearance of 54.5 mL/min. Valproic acid elimination half-life was 3 h during the 190 min hemoperfusion cycle. Posthemoperfusion elimination half-life was 4.8 h with continued multiple-dose activated charcoal dosing. The clinical condition improved during hemoperfusion.

Enteric coated valproic acid preparations may cause delayed toxicity in overdose, particularly with coingested anticholinergic medications. In our case, charcoal hemoperfusion appeared to increase valproic acid clearance.