Monitoring phenytoin level ensures treatment is both safe and effective.
Phenytoin level Overview
Phenytoin is used for the management of tonic-clonic (grand mal) and complex partial seizures, and for prevention of seizures following head trauma or neurosurgery.
Phenytoin level is measured in microgram/milliliters (mcg/mL).
The therapeutic range for phenytoin is 10–20 mcg/mL.
- Toxic level: 25-50 mcg/mL
- Lethal level: >100 mcg/mL
What the results mean
A level that is higher than normal is usually due to a change in formulation or drug interaction. A high phenytoin level may require a reduction in dose. Some symptoms of toxicity include: ataxia, dizziness, nystagmus, diplopia, and paradoxical seizures.
A low phenytoin level may require an increase in phenytoin dose. A low phenytoin level may be caused by an absorption problem. This becomes important in young infants (younger than 3 months) or in patients given phenobarbital, charcoal, or antacids at the same time as phenytoin. A low phenytoin level may be associated with noncompliance.