Phenytoin is used as both an abortive and preventive medication in seizure management.
The total phenytoin reference range varies by age, as follows:
Children and adults: 10-20 µg/mL
Neonates: 8-15 µg/mL
Toxic phenytoin levels are defined as greater than 30 µg/mL.
Lethal levels are defined as greater than 100 µg/mL.
The reference range of free phenytoin is 1-2.5 µg/mL.
In patients with renal failure associated with hypoalbuminemia, free phenytoin levels may be more accurate than total phenytoin levels.
However, the Sheiner-Tozer formula (below) can be used to correct the phenytoin level.
Adjusted concentration = measured total concentration / [(0.2 x albumin) + 0.1]