What is the Winter-Tozer equation for phenytoin correction?

Corrected phenytoin = Observed phenytoin / (0.2 × albumin + 0.1) for normal renal function. For renal failure (CrCl <10 mL/min): corrected = Observed / (0.1 × albumin + 0.1). Normal albumin assumed at 4.4 g/dL. Target corrected total phenytoin: 10–20 mg/L (free: 1–2 mg/L).

When should free phenytoin level be measured directly?

Direct free phenytoin is preferred when: albumin <2 g/dL (formula less reliable), dialysis patients (unpredictable protein binding), critical illness with rapidly changing albumin, suspected drug interactions affecting protein binding, or when corrected total level is discordant with clinical response.

Phenytoin Free Level Correction for Albumin

Correct measured total phenytoin level for hypoalbuminemia or renal failure using Winter-Tozer equation to estimate free phenytoin and avoid dose adjustment errors.

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Phenytoin Free Level Correction for Albumin

Frequently Asked Questions

What is the Winter-Tozer equation for phenytoin correction?

When should free phenytoin level be measured directly?