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

Input:
Phenytoin Measured
Serum Albumin
Result:
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.
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