Labs & Drug Levels

Phenytoin Corrected for Albumin (Sheiner-Tozer) Calculator

Estimates what a total phenytoin level would be at normal albumin, with the end-stage renal disease version.

Reviewed by Alex G, BSN, RN, CEN, CCRN, CMC, NREMT-P · From the Reference tab of the app

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Formula

Corrected total = measured total ÷ (0.2 × albumin + 0.1)
End-stage renal disease (creatinine clearance under 10 mL/min): measured total ÷ (0.1 × albumin + 0.1)
Revised coefficient: measured total ÷ (0.29 × albumin + 0.1)
Phenytoin in mcg/mL (= mg/L), albumin in g/dL; the free level is about 10% of the corrected total

Reference: Normal 10–20

How it is used

• Usual total range 10–20 mcg/mL (Patsalos 2008); about 10% is normally unbound, so the free range is about 1–2 mcg/mL.
• The equations are biased and imprecise in critically ill, trauma and neurology patients, and with low albumin plus kidney dysfunction no coefficient was reliable: send a free level (Kiang & Ensom 2016; Montgomery 2019).
• A revised coefficient of 0.29 in place of 0.2, derived in neurocritical care, gives lower corrected values and is shown in the label for comparison (Kane 2013).
• The end-stage renal disease version missed by more than 50% in two thirds of samples in a 2017 cohort (Soriano 2017): measure free phenytoin in kidney failure.

Key points

• Do not raise the dose for a low total level in a patient with low albumin until a corrected or, better, a measured free level is known: the active free drug may already be high.

Same formula as the app. Open it in the web app.

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For education and exam preparation only. Follow your institution’s protocols. For education and exam preparation only. Verify results independently and follow your institution’s protocols. Not a substitute for clinical judgment.