Phenytoin Level Correction Calculator

How to Use This Calculator

Enter the measured total phenytoin level and the concurrent albumin level. Choose the renal function that best reflects the patient’s clearance and click Calculate to reveal the corrected concentration.

The result updates immediately and can be compared against therapeutic targets or historic labs.

Methodology

This tool follows the Sheiner-Tozer correction. It assumes that albumin-bound phenytoin is unavailable and that renal impairment reduces the scaling coefficient to 0.10, otherwise 0.20. The reference for this approach is MDCalc’s albumin and renal failure correction guide. We keep all calculations transparent so you can review inputs, factors, and outputs.

• The denominator equals the chosen factor times the albumin level plus 0.1, imitating the Sheiner-Tozer binding adjustment.
• Normal renal function uses factor 0.20; impaired uses 0.10 to reflect slower clearance.
• Results are rounded to two decimal places and expressed in mg/L for consistent reporting.

Step-by-step Example

For a patient with a total phenytoin level of 15 mg/L, an albumin level of 3.5 g/dL, and normal renal function, the denominator is 0.2 × 3.5 + 0.1 = 0.8. The corrected phenytoin level becomes 15 ÷ 0.8 = 18.75 mg/L, which helps guide dosing when albumin is low.

Glossary of Variables

• Total Phenytoin Level: The measured total drug concentration in the serum.
• Albumin Level: Serum albumin concentration; lower levels free up more phenytoin.
• Corrected Phenytoin Level: The albumin- and renal-adjusted concentration used for therapeutic decisions.

Frequently Asked Questions