Correlation of Free and Total Phenytoin Serum Concentrations in Critically Ill Patients

Background: Phenytoin is a common medication for seizure treatment and prophylaxis in the intensive care unit (ICU). The clinical utility of the Sheiner-Tozer equation for adjusting total phenytoin levels for hypoalbuminemia remains controversial. Objective: The purpose of this study was to evaluate the correlation of this formula in predicting phenytoin serum concentrations. Methods: A retrospective cohort study was conducted in the adult ICU between January 1, 2010, and June 21, 2013. Patients meeting the following study criteria were included: age ≥18 years, admission to the ICU, simultaneously drawn total and free serum phenytoin concentrations with albumin ≤48 hours of phenytoin draws. Study end points were the correlation as well as the level of agreement in the interpretation of the free and adjusted phenytoin concentrations using the Sheiner-Tozer formula in critically ill patients with hypoalbuminemia. Results: A total of 238 patients were analyzed. Mean adjusted total phenytoin and free levels w...