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Valproic Acid (VPA)

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EPIC Test Name

VALPROIC ACID LEVEL, TOTAL

EPIC Code

LAB24

Specimen Requirements

plasma
Minimum Volume:0.5 mL
Collection:Collect using standard laboratory procedures
Transport:Room Temperature ASAP
Stability:Room Temperature: 2 days capped at 15-25 degrees C
Refrigerated: 7 days capped at 2-8 degrees C
Frozen: 3 months capped at -20 degrees C
Avoid repeat freezing and thawing
Container:LIT-GRN
Rejection Causes:Insufficent Sample Volume

Methods

Homogeneous enzyme immunoassay

Turnaround Time

SpecimenTurnaround TimeFrequency
plasmaStat: 90 minutes Routine: 4 hours24/7

Reference Ranges

Homogeneous enzyme immunoassay
UnitCritical ValuesTherapeutic Levels
µg/mL>120 ug/mL50-100 µg/mL

Clinical Indications

Valproic acid (valproate, Depakote, or Depakene) is an effective medication for absence seizures, generalized tonic-clonic seizures, and partial seizures, when administered alone or in conjunction with other antiepileptic agents. It also has mood-stabilizing effects that make it a useful agent in the treatment of bipolar disorder.
Valproic acid inhibits the enzyme GABA transaminase, resulting in an increase in the concentration of GABA in the brain. GABA is a potent inhibitor of discharges in the central nervous system. It also modulates the synaptic sodium channel by prolonging inactivation, which reduces the ability of the neuron to respond at high frequency. Additional mechanisms of action have been reported, such as GSK-3 activity that might explain its utility in mood disorders.
The valproic acid that circulates in blood is around 90% protein-bound under normal circumstances. In uremia or during concomitant therapy with other drugs that are highly protein-bound (such as phenytoin), valproic acid is displaced from protein, resulting in a higher free fraction of the drug circulating in blood. As a result, even the total drug concentration may be within the therapeutic range, the portion of the free drug may be in toxic level. Because the pharmacokinetics of the drug can be extensively influenced by other drugs, e.g., phenobarbital, phenytoin and lamotrigine, proper dose adjustment and monitoring its blood concentration are important to avoid adverse event and toxicity.

Common Synonyms

Depakote, Depakene Depakane, Depakene, Depakote, Divalproex

Performed

Lab
Chemistry - Community
Chemistry - Downtown

Interpretative Information

The range for therapeutic concentration of total valproic acid is 50 to 100 mcg/mL.
Low valproic acid concentration relative to these ranges may suggest inadequate dosing, while a high valproic acid concentration may be associated with hepatic toxicity and acute toxic encephalopathy.
Because the concentration of valproic acid fluctuates considerably depending on the time from last dose, interpretation of the clinical significance of the valproic acid concentration must take into consideration the timing of the blood specimen. The ideal time for monitoring the blood concentration is to drawn just before the next dose, to confirm that an adequate dose has been prescribed.

CPT

80164

LOINC

4086-5

References

1. Ghodke-Puranik Y, Thorn CF, Lamba JK, Leeder JS, Song W, Birnbaum AK, Altman RB, Klein TE. Valproic acid pathway: pharmacokinetics and pharmacodynamics. Pharmacogenet Genomics. 2013 Apr;
2. Michael C. Milone and Leslie M. Shaw: Therapeutic Drugs and Their Management. In: Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier Saunders; 2018:813-815
3. Marzinke A and Clarke W. Antiepileptic drugs. In The Clinical Toxicology Laboratory – contemporary practice of poisoning evaluation. ed. by Tai Kwong, etc., 2nd ed. Page 235-60.

Contact Information

Chemistry - Downtown: (315)464-4460
Chemistry - Community: (315)492-5531
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