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Phenytoin (Dilantin) Albumin Correction Calculator (Winter-Tozer)

Calculate serum Phenytoin (Dilantin) corrected total concentrations adjusting for hypoalbuminemia and end-stage renal disease (ESRD) using the Sheiner-Tozer equation.

Standard therapeutic target: 10 - 20 mcg/mL
Normal baseline = 4.4 g/dL

Calculation Results

Corrected Total Phenytoin: 15.7 mcg/mL Therapeutic Range (10 - 20 mcg/mL)
Estimated Free Unbound Phenytoin: 1.57 mcg/mL (Therapeutic free target: 1.0 - 2.0 mcg/mL)
Clinical Warning: Apparent Low Level was Pseudo-Subtherapeutic!
Equation Formula Applied: Winter-Tozer Normal Renal: C / (0.2 * Alb + 0.1)

About This Calculator

Calculate serum Phenytoin (Dilantin) corrected total concentrations adjusting for hypoalbuminemia and end-stage renal disease (ESRD) using the Sheiner-Tozer equation.

Frequently Asked Questions

Why does hypoalbuminemia distort measured phenytoin levels?

Phenytoin is 90% bound to plasma albumin; only the 10% unbound (free) fraction is pharmacologically active. When serum albumin drops, less drug binds and the free fraction rises. Total lab phenytoin appears deceptively low even though free active drug is fully therapeutic.

What is the Winter-Tozer equation formula?

The standard formula for patients with normal renal function is: Corrected Total Phenytoin = Measured Total / [(0.2 x Albumin) + 0.1]. For patients with ESRD or CrCl < 10 mL/min, the formula modifies to Measured Total / [(0.1 x Albumin) + 0.1].

What is the therapeutic reference range for phenytoin?

Total serum phenytoin therapeutic range is 10 to 20 mcg/mL. The unbound free phenytoin therapeutic range is 1.0 to 2.0 mcg/mL.

What clinical danger occurs if a doctor does not correct for albumin?

A clinician seeing an unadjusted lab reading of 8.0 mcg/mL might mistakenly increase the dose, precipitating severe toxicity (nystagmus, ataxia, cerebellar dysfunction, confusion) because the patient's true active free level was already therapeutic.