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    Phenytoin (Dilantin) Correction for Albumin / Renal Failure

    Corrects serum phenytoin level for renal failure and/or hypoalbuminemia.
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    INSTRUCTIONS

    Use in patients with albumin ≤3.2 g/dL (32 g/L). The “Sheiner-Tozer Equation” is the official name of this correction. This updated formula uses an albumin coefficient of 0.275, and 0.2 for patients with renal failure (see Evidence for details).

    When to Use
    Pearls/Pitfalls
    Why Use

    Patients taking phenytoin who have renal failure or albumin ≤3.2 g/dL (32 g/L).

    Phenytoin has a narrow therapeutic window, and is highly protein-bound. The protein-bound phenytoin is what is typically measured by the lab. However, unbound phenytoin is the active portion (it crosses the blood-brain barrier). This calculator helps estimate the equivalent active amount of phenytoin based on typical lab values.

    Helps avoid under- or over-dosing in patients with renal failure or low albumin.

    µg/mL
    g/dL
    No
    Yes

    Result:

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    Next Steps
    Evidence
    Creator Insights

    Advice

    • Adjust phenytoin dosing based on values.

    • If consistently out of range, consider other antiepileptics.

    • Concomitant use of valproic acid and some other drugs displaces phenytoin from plasma proteins and can lead to erratic levels.

    • Whenever possible, a free phenytoin level should be utilized over a corrected level.

    Critical Actions

    A therapeutic phenytoin level is generally considered to be 10-20 mg/L (40-80 µmol/L). Levels above this may cause nystagmus, ataxia, lethargy, confusion, and coma.

    Content Contributors
    • Andrew Michalak, MD
    About the Creator
    Dr. Thomas N. Tozer
    Are you Dr. Thomas N. Tozer?
    Content Contributors
    • Andrew Michalak, MD