Phenytoin and Dilantin: Same Medication
Yes, phenytoin and Dilantin are the same medication—Dilantin is simply the brand name for phenytoin. 1, 2
Key Points About Nomenclature
- Phenytoin is the generic drug name (active pharmaceutical ingredient) 2
- Dilantin is the brand name manufactured originally by Parke-Davis (now Pfizer) 2
- Both terms refer to the same antiepileptic medication used to treat seizures 1, 2
Important Clinical Distinctions
While the active ingredient is identical, there are critical formulation differences you must understand:
Formulation Variations
- Dilantin Kapseals (extended phenytoin sodium capsules): Contains the sodium salt form 2
- Generic phenytoin: May be formulated as either sodium salt or free acid 2
- Free acid form (found in Dilantin-125 Suspension and Dilantin Infatabs): Contains approximately 8% more drug content than the sodium salt formulation 2
Clinical Implications of Brand-to-Generic Interchange
When switching between brand and generic formulations, serum level monitoring is essential due to phenytoin's narrow therapeutic index and nonlinear kinetics. 2, 3
- One study documented 22-31% lower serum phenytoin levels when patients switched from Dilantin to a specific generic formulation 3
- However, a more recent study of 222 patients showed no increased seizure events when switching from Dilantin Kapseals to an AB-rated generic equivalent, despite detecting more low serum concentrations post-interchange 4
- The FDA requires AB-rated generics to demonstrate bioequivalence, but real-world variability can occur 4, 3
Dosing Considerations
The therapeutic serum level range is 10-20 mcg/mL for both brand and generic formulations. 2
Standard Adult Dosing
- Initial: 100 mg three times daily 2
- Maintenance: 300-400 mg daily in divided doses 2
- Once-daily dosing: Only recommended with Dilantin extended capsules (300 mg) after seizure control is established 2
Loading Dose Strategy
- Oral loading: 1 gram divided into three doses (400 mg, 300 mg, 300 mg) at two-hour intervals 2
- IV loading: 18-20 mg/kg at maximum rate of 50 mg/min 1
Critical Safety Caveat
Only Dilantin extended phenytoin sodium capsules are FDA-approved for once-daily dosing. 2 Generic formulations have inherent differences in dissolution characteristics that preclude automatic substitution for once-daily regimens without careful monitoring. 2
When any dosage form or brand change occurs, close monitoring of phenytoin serum levels is mandatory to prevent loss of seizure control or toxicity. 2, 4