Below the range
Common causes of a low Phenytoin Level
- Nonadherence
- Enzyme-inducing drugs
Looking for the other direction? See what causes a high Phenytoin Level.
All tests · Therapeutic Drug Levels · Phenytoin Level
Below the range
What causes a low Phenytoin Level?
Normal range 10-20 µg/mL (40-79 µmol/L SI). Specimen: Serum (trough). See the full Phenytoin Level reference page for critical values and nursing considerations.
What is the normal range for Phenytoin Level?
The standard teaching reference range for Phenytoin Level is 10-20 µg/mL in conventional units, or 40-79 µmol/L in SI units. This value is measured in serum (trough).
| Specimen | Serum (trough) |
|---|---|
| Conventional range | 10-20 µg/mL |
| SI range | 40-79 µmol/L |
| Critical value | > 20 µg/mL (nystagmus, ataxia); > 30 confusion |
| Panel | Therapeutic Drug Levels |
Full details, including nursing considerations, on the Phenytoin Level normal range page. Reference ranges vary by laboratory, method, age, sex, and population - always use the range printed on the actual result.
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