Phenytoin correction for low albumin (Sheiner-Tozer)
Estimates the total phenytoin level a patient with normal albumin would have, including the end-stage kidney disease variant.
Inputs
0 of 3Kidney function
When to use
- A total phenytoin level in a patient with albumin below about 3.5 g/dL.
- End-stage kidney disease, where uremia also displaces phenytoin.
Pearls and pitfalls
- A measured free phenytoin level (target 1 to 2 mg/L) is more reliable than any correction, especially in the critically ill.
- The equation tends to underestimate the true free fraction in ICU patients.
- Valproate also displaces phenytoin; use the valproate-adjusted calculator.
Why use
Low albumin raises the free fraction, so a 'low' total level can be therapeutic or even toxic.
Corrected = measured ÷ (x × albumin + 0.1); x = 0.2 normally, 0.1 if CrCl < 10 mL/min