- Phenytoin has a wide volume of distribtuion and is 90% bound to protein.
- Only the unbound proportion is biologically active, and therefore, FREE levels of phenytoin should be checked to determine whether acute seizure activity is related to suboptimal levels or not.
- Given these properties, patients with the following conditions are more likely to become phenytoin toxic: neonates and the elderly (due to poor metabolism and low protein production); uremia, nephrotic syndrome, pregnancy, malignancy, malnutrition (due to low potein levels).
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