Phenytoin Level Correction (Sheiner-Tozer)

Correct measured phenytoin level for hypoalbuminemia and/or renal failure.

For educational and clinical reference. Not a substitute for medical judgment. See the medical disclaimer.
Corrected phenytoin level
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References

  1. Sheiner LB, Tozer TN. Clinical pharmacokinetics: the use of plasma concentrations of drugs. In: Clinical Pharmacology: Basic Principles in Therapeutics. 1973.

How to use

  1. Enter measured total phenytoin level and serum albumin.
  2. Check the ESRD box if CrCl < 20 mL/min.
  3. Corrected level appears instantly.

Frequently asked questions

Formula?

Sheiner-Tozer: Corrected level = Measured / (0.2 × albumin + 0.1). In ESRD/CrCl < 20: divisor uses 0.1 × albumin + 0.1.

Why correct?

Phenytoin is ~90% albumin-bound. In hypoalbuminemia, the total (measured) level underestimates the free (active) level, risking subtherapeutic decisions when free level is actually adequate.

Therapeutic range?

Total phenytoin: 10–20 mcg/mL. Free phenytoin: 1–2 mcg/mL (when available).

Limitations?

Sheiner-Tozer over-estimates in some populations. Direct measurement of free phenytoin is preferred when feasible.

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