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Test Name:
Valproic Acid, Free
- SBMF No:
29075 - Performance Lab Name:
Automated Lab - Test Mnemonic:
VALP FREE - ABN:
Not required - CPT Code:
80164 - LOINC Code:
4087-3 - Also Known As:
Depakene®
Depakote®
Unbound Valproic Acid - Also See:
31032 Valproic Acid, Total - Spec Type:
Serum - Spec Container:
Red top (serum) tube - Alt Spec Type:
Plasma - Alt Spec Container:
Lavender top (EDTA) tube - Pref Vol:
1.0 mL - Min Vol:
0.5 mL - Fasting:
No - Spec Collect:
Do not use gel-barrier tubes for specimen collection
Routine venipuncture
Trough level: collect immediately before next dose
Peak level: collect 1-3 hours following a dose - Spec Process:
Serum sample tubes, clot 30 minutes
Promptly centrifuge 15 minutes
Immediately transfer serum or plasma to separate plastic tube and freeze - Spec Store Transport:
Frozen - Spec Stability:
8 hours room temperature (20-30°C)
2 weeks frozen (-20°C) – Do not use frost-free units that undergo repeated freeze/thaw cycles - Methodology:
Fluorescence Polarization - Use:
Detect use
Evaluate therapeutic effect or possible toxicity - Clinical Significance:
Valproic acid is a broad-spectrum anticonvulsant drug used solely or in combination with other anticonvulsant drugs for the treatment of absence seizures. It also has demonstrated effectiveness in the management of generalized tonic-clonic and myoclonic seizures, as well as atypical absence, simple and complex partial and mixed grand mal and petit mal seizures. The capability of treating many types of seizures with a single anticonvulsant has resulted in the widespread use of valproic acid, particularly in children in whom tonic-clonic and myoclonic seizures are most prevalent. Valproic acid has proven effective in the treatment of many patients otherwise refractory to other anticonvulsant treatments. Most patients receiving valproic acid do not develop a tolerance to its anticonvulsant effects.
Valproic acid is rapidly absorbed orally with syrup peak levels reached in 15 minutes to 2 hours. Absorption of enteric-coated diavalproex is delayed one hour with peak levels occurring 1 to 4 hours after a single oral dose.
Free Valproic Acid serum levels should be obtained on the following occasions:
Two to four days following initiation of therapy
Two to four days following any change in valproic acid dosage or dosing interval
When other antiepileptic drugs are added or withdrawn
If a decrease in seizure control occurs
If physical or laboratory signs of toxicity occur
When noncompliance is suspectedTime to peak concentration varies with food intake and preparation:
Fasting:
– Syrup: 0.5-1 hour
– Capsule: About 2 hours
Non-fasting:
– Syrup: About 3 hours
– Capsule: About 8 hours - Reference Range:
5.0-20.0 µg/mL (this reference range is calculated from the therapeutic range of valproic acid that is approximately 10-20% unbound) - Day Run:
Sun-Sat (daily) - Time Run:
As received - Time Reported:
8 hours - Test Type:
TOX-TDM
