Phenytoin Free (Unbound) Drug Level (Adjusted for Hypoalbuminemia)

Phenytoin Measured
Serum Albumin
Phenytoin Free
Decimal Precision:
PhenytoinFree = (0.55 * PhenytoinMeasured / SerumAlbumin) - 0.14
  • This calculator is used to predict the pharmacologically active unbound phenytoin level (free fraction) in patients with hypoalbuminemia.
  • To predict the total phenytoin level commonly used for phenytoin dosage adjustment, please see the calculator Phenytoin Total Drug Level (Adjusted for Hypoalbuminemia and Renal Function.)
  1. Dasgupta A, Dennen DA, Dean R, McLawhon RW. Prediction of free phenytoin levels based on [total phenytoin]/[albumin] ratios. Potential errors with hypoalbuminemia. Am J Clin Pathol. 1991 Feb;95(2):253-6.
  2. Martin E, Tozer TN, Sheiner LB, Riegelman S. The clinical pharmacokinetics of phenytoin. J Pharmacokinet Biopharm. 1977 Dec;5(6):579-96.
Legal Notices and Disclaimer
All information contained in and produced by the MedCalc 3000 system is provided for educational purposes only. This information should not be used for the diagnosis or treatment of any health problem or disease. THIS INFORMATION IS NOT INTENDED TO REPLACE CLINICAL JUDGMENT OR GUIDE INDIVIDUAL PATIENT CARE IN ANY MANNER. Click here for full notice and disclaimer.
MedCalc 3000 is Copyright © 1998-2011 Foundation Internet Services, LLC    [Build 244179 v11.2.2]