Valproic acid (VPA) often is used to treat mania in bipolar disorder, and it has a therapeutic range of 50 to 125 µg/mL of total serum concentration.1 VPA binds highly to albumin, resulting in free drug concentrations (5 to 15 mg/L) that are responsible for its therapeutic effect.2 Monitoring total VPA levels in patients with hypoalbuminemia could reveal seemingly subtherapeutic VPA levels, which could lead to unnecessary dosage adjustments or drug toxicity. Hermida et al3 devised a correction equation to normalize total VPA serum concentrations <75 µg/mL in patients with hypoalbuminemia (Table 1, Box).
We present a case employing this equation in a patient
Case
Ms. T, age 75, is admitted to the hospital with delusional, paranoid, assaultive, and combative behavior. By applying Ms. T’s baseline lab findings (Table 2) to the equation, a normalized total VPA level and estimated free VPA level of 70 µg/mL and 7 µg/mL, respectively, can be approximated. These estimates fall within the therapeutic range and are validated by the measured free VPA level of 9 µg/mL.
VPA serum levels should be assessed 2 to 4 days after initiation or dosage adjustments.1 Also, consider patient-specific goals and intended clinical effect when adjusting VPA dosage. In practice settings, where free VPA levels are not routinely monitored or are cost prohibitive, this equation can guide clinical decision-making.3