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Abstract
Objective To test the accuracy of an equation in adult patients with status epilepticus that calculates the free concentration of serum valproic acid (fVPA) from the total concentration of serum valproic acid (tVPA) and serum albumin.
Methods All adult patients with status epilepticus who were treated at a Swiss academic medical center between 2005 and 2018 with concurrent measurements of tVPA, fVPA, and serum albumin were included. fVPA was categorized as subtherapeutic, therapeutic (5–10 mg/L), or supratherapeutic. Agreement was defined as the proportion of measured and calculated fVPA falling within the same category.
Results Of 676 patients with status epilepticus, 104 had 506 measurements, with a median of 3 (interquartile range [IQR] 1.5–6.5) per patient. The median tVPA was 43.5 mg/L (27.4–63.6), with measured fVPA 9.1 mg/L (4.5–14.7) and calculated fVPA 10.1 mg/L (7.0–13.0), respectively. The median deviation of calculated from measured fVPA was −0.8 mg/L (−3.2 to 2.5) with 336 measurements >1 mg/L. While the association between measured and calculated fVPA was linear (regression coefficient 1.1, 95% confidence interval 0.9–1.2, p < 0.0001), the agreement on effective drug levels did not match in 39.8% of measurements regardless of serum albumin levels, with calculated fVPA overestimating measured fVPA in 30.4%. tVPA and serum albumin independently influenced the accuracy of the calculated fVPA in the multivariable model.
Conclusions Calculated fVPA is inaccurate when using the proposed equation in adult patients with status epilepticus, calling for drug monitoring based on measured fVPA in this context.
Glossary
- ASD=
- antiseizure drug;
- BUN=
- blood urea nitrogen;
- CI=
- confidence interval;
- fVPA=
- free valproic acid serum concentration;
- ICU=
- intensive care unit;
- IQR=
- interquartile range;
- STEP UP=
- Status Epilepticus Unicenter Population;
- tVPA=
- total valproic acid serum concentration;
- VPA=
- valproic acid
Footnotes
Go to Neurology.org/N for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
- Received April 27, 2020.
- Accepted in final form August 20, 2020.
- © 2020 American Academy of Neurology
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