Valproic Acid, Serum or Plasma

Casandra

Casandra Test Code LC79662Version 1 (DRAFT)

Performing Lab

Lab LabcorpLab Test ID 007260CPT Code 80164

Valproic Acid, Serum or Plasma

Also known as: Depacon®, Depakene®, Depakote®, Stavzor™, Valproate

Clinical Use

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Use

Valproate (valproic acid; divalproex sodium, a compound containing sodium valproate and valproic acid) controls absence, myoclonic, and tonic-clonic seizures in generalized, idiopathic, and symptomatic epilepsy. It is most useful in typical absence seizures. Valproate is as effective as ethosuximide in patients with absence seizures alone and is variably effective in atypical absence seizures. Although some clinicians prefer valproate for absence seizures, the American Academy of Pediatrics (Committee on Drugs, 1982) recommended that it be reserved for use when therapeutic failure or intolerance to ethosuximide occurs, because valproate causes rare but potentially fatal hepatotoxicity. Many neurologists consider valproate the drug of choice for patients with both absence and other generalized seizure types, including tonic-clonic convulsions. Its efficacy is about the same as in patients with the latter type alone.

Special Instructions

Hepatotoxicity due to valproate is idiosyncratic and not preventable by routine liver enzyme monitoring. In very young children on multiple anticonvulsants, valproate-induced cytopenias warrant monitoring of complete blood counts. Pregnant women in their first trimester should be cautious due to a risk of neural tube defects. Valproate binds to plasma proteins in a saturable manner; usual effective plasma concentrations range from 50−120 μg/mL. Valproate is extensively metabolized by the liver, and its antiepileptic activity is not well correlated with steady-state plasma concentrations.

Limitations

Routine liver enzyme monitoring cannot prevent hepatotoxicity, which occurs idiosyncratically in very young children, usually those on multiple anticonvulsants. Valproate-induced cytopenias may be dose-related. Monitoring for hyperammonemia without liver function test abnormalities is necessary, as encephalopathy can occur. The antiepileptic activity duration does not directly correlate with plasma concentrations, and several metabolites are involved, with potential contributions to both therapeutic and adverse effects.

Test Details