Valproic Acid

VALP

Depakote

Serum (gold top) tube

0.5 mL

Lithium Heparin Plasma (green top) tube

Valproic acid monitoring is most appropriate when the blood sample is drawn after steady-state conditions have been reached (after 4–5 half-lives on an unchanged dose regimen).  For patients receiving valproic acid orally the blood sample should be drawn immediately before the next dose because of its short half-life.  Valproic acid samples should be monitored at a consistent time of day because concentration is affected by circadian rhythm.

Serum (gold top) tube or Lithium Heparin Plasma (green top) tube

Room Temperature or Refrigeration

Room Temperature - 1 day; Refrigeration - 14 days

Quantity Not Sufficient, IV Contamination

Daily upon receipt

Upon completion of analysis

Achieving and maintaining therapeutic concentrations of valproic acid is difficult due to inter- and intra-patient variability in pharmacokinetics. Valproic acid pharmacokinetics are affected by disease states or coadministered drugs that affect clearance or protein binding of valproic acid; age; alcohol and other central nervous system depressants; pregnancy; renal failure and liver disease or dysfunction. The therapeutic range concentrations depend on whether mono- or polytherapy is being used. The upper end of the therapeutic range for valproic acid is not well defined. The therapeutic endpoint is the abolition of seizures. The dose given to patients may continue to be increased in patients who do not experience side effects. The total measured serum or plasma concentration of valproic acid will increase linearly with dose up to the point of saturation of the protein binding sites. The unbound (free) concentration of valproic acid increases rapidly above this

Therapeutic Range:  50 - 120 ug/mL

Valproic acid is used as sole or adjunctive therapy in the treatment of simple and complex absence seizures, and adjunctively in patients with multiple seizure types, which include absence seizures. High concentrations of valproic acid may lead to central nervous system depression, tremor, and thrombocytopenia. Very high concentrations of valproic acid may also increase the risk of developing fatal hepatotoxicity, stupor, coma, or cerebral edema.  Valproic acid is extensively etabolized by the liver. Other coadministered drugs, including other antiepileptics, may induce or inhibit the drug metabolizing enzymes of the liver. When these drugs are added or removed from the therapeutic regimen of a patient, the clearance and concentration of valproic acid may be altered, requiring dosage adjustment.  Serum or plasma valproic acid measurements are used in the diagnosis and treatment of valproic acid overdose and in monitoring levels of valproic acid to ensure appropriate therapy.