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Albumin-corrected phenytoin level calculator (Sheiner-Tozer)

Corrects a total phenytoin level for low serum albumin with the Sheiner-Tozer equation (1978), and compares it with the usual total range of 10 to 20 mg/L. A variant for severe kidney failure is included.

  • Body size and dosing
  • Sheiner-Tozer
  • Runs on your device

Short answer

The Sheiner-Tozer equation (1978) corrects a total phenytoin level for low albumin: measured level ÷ (0.2 × albumin in g/dL + 0.1). For severe kidney failure or dialysis the 0.2 is replaced by 0.1.

Albumin-corrected phenytoin level

Runs on your device. Nothing you enter is saved or sent.

Estimate only. Interpret it with the patient's clinical picture and the product label.

Sources

2
  1. Sheiner LB, Tozer TN. Clinical pharmacokinetics: the use of plasma concentrations of drugs. In: Melmon KL, Morrelli HF, eds. Clinical Pharmacology: Basic Principles in Therapeutics, 2nd ed. New York: Macmillan; 1978:71–109. Not indexed in PubMed
  2. Kiang TKL, Ensom MHH. A comprehensive review on the predictive performance of the Sheiner-Tozer and derivative equations for the correction of phenytoin concentrations. Ann Pharmacother. 2016;50(4):311–325. DOI 10.1177/1060028016628166 PubMed 26825643

Formula version: Albumin-corrected phenytoin (Sheiner-Tozer) · MediHelp calc v1.3.1

Formula and sources checked on 2026-11-02

When this estimate is not valid

5
  • A free (unbound) phenytoin level is more reliable than any correction when it is available.
  • The Sheiner-Tozer equation is an estimate and can be inaccurate, particularly in critical illness, so use it only as a guide.
  • Derived with older albumin assays: with modern assays the 0.2 equation tends to overestimate the corrected level, and revised coefficients (0.25 to 0.275) have been proposed. Treat the result as an upper estimate.
  • Needs a steady-state level taken at the right time after the dose.
  • The usual total range is 10 to 20 mg/L. Clinical response matters more than the number.

Estimate only. Interpret it with the patient's clinical picture and the product label.

About this calculator

What it is
The Sheiner-Tozer equation estimates what a total phenytoin level would be with a normal albumin.
Why it is used
Phenytoin is highly protein-bound, so a low albumin lowers the total level while the free (active) level is unchanged, which can lead to unnecessary dose increases.
How to use it
Enter a steady-state total phenytoin level and the albumin from the same time; mark end-stage kidney disease (CrCl under about 20 mL/min), which uses the 0.1 coefficient.
How to read the result
Read the corrected level against the usual total range of 10 to 20 mg/L (40 to 80 µmol/L), which corresponds to a free level of 1 to 2 mg/L. It is an estimate that tends to overestimate with modern albumin assays; a measured free level is better when available, and clinical response matters more than the number.

How it is calculated

C normalised = C measured ÷ (0.2 × albumin + 0.1) · albumin in g/dL

The measured total level is divided by an albumin factor. Albumin is in g/dL; a value in g/L is divided by 10 first.

with severe renal failure: ÷ (0.1 × albumin + 0.1)

For severe kidney failure (creatinine clearance under 10 mL/min) or dialysis, the calculator uses the Sheiner-Tozer variant with 0.1 in place of 0.2.

A phenytoin level in µmol/L is divided by 3.964 to give mg/L, and the corrected value is also shown in µmol/L.

The corrected level is compared with the usual total range: below 10 mg/L, 10 to 20 mg/L, or above 20 mg/L. Clinical response matters more than the number.

Limits: phenytoin 0.5–100 mg/L and albumin 1–6 g/dL. The equation needs a steady-state level taken at the right time after the dose, and it was derived with older albumin assays (Kiang 2016).

Worked example

A total phenytoin level of 8 mg/L with an albumin of 2 g/dL and no severe kidney failure:

  1. 0.2 × 2 + 0.1 = 0.500
  2. 8 ÷ 0.500 = 16.0 mg/L

Corrected phenytoin level 16.0 mg/L (albumin factor 0.500), which is within the usual range of 10 to 20 mg/L. The same value is 63 µmol/L.

Questions

Is a free phenytoin level better than this correction?

Yes. A free (unbound) phenytoin level is more reliable than any correction when it is available.

How accurate is the Sheiner-Tozer equation?

It is an estimate and can be inaccurate, particularly in critical illness, so use it only as a guide.

Why treat the result as an upper estimate?

The equation was derived with older albumin assays. With modern assays the 0.2 equation tends to overestimate the corrected level, and revised coefficients (0.25 to 0.275) have been proposed (Kiang 2016).

What range is the corrected level compared with?

The usual total range of 10 to 20 mg/L. Clinical response matters more than the number, and the level must be a steady-state level taken at the right time after the dose.

Use the calculators in the MediHelp app

Estimate only. Interpret it with the patient's clinical picture and the product label.