Normal Reference Ranges
Adult
Therapeutic: 10 - 20 mcg/mL
Pediatric
Therapeutic: 10 - 20 mcg/mL
Clinical Significance
Anti-epileptic drug with zero-order (non-linear) kinetics at higher doses. Must adjust for low albumin (calculate free phenytoin).
Causes of High
- Toxicity (causes nystagmus, ataxia, lethargy)
Causes of Low
- Non-compliance
- Subtherapeutic dosing (risk of seizures)