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Phenytoin / Fosphenytoin Dosing
Loading dose, maintenance, and albumin-corrected level (Winter-Tozer)
Patient Parameters
Required (20–300)
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Loading Dose
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Maintenance (mg/day)
| Parameter | Target / Dose | Notes |
|---|---|---|
| Status Epilepticus Load | Fosphenytoin 20 mg PE/kg IV | Max rate 150 mg PE/min |
| Phenytoin IV Load | 15–20 mg/kg IV | Max rate 50 mg/min; cardiac monitor required |
| Maintenance (adults) | 4–6 mg/kg/day | Divide Q8–12h or once daily ER |
| Therapeutic range (total) | 10–20 mcg/mL | Draw trough level |
| Therapeutic range (free) | 1–2 mcg/mL | Use free level in hypoalbuminemia |
Winter-Tozer Correction (normal renal): Corrected = Measured / [(0.2 × albumin) + 0.1]
Winter-Tozer Correction (dialysis): Corrected = Measured / [(0.1 × albumin) + 0.1]
Loading dose: 20 mg PE/kg (status epilepticus) or 15 mg/kg (prophylaxis)
Winter-Tozer Correction (dialysis): Corrected = Measured / [(0.1 × albumin) + 0.1]
Loading dose: 20 mg PE/kg (status epilepticus) or 15 mg/kg (prophylaxis)
Safety: IV phenytoin must be given with cardiac monitoring (risk of hypotension, bradycardia). Fosphenytoin is preferred (faster, safer). Phenytoin has non-linear (zero-order) pharmacokinetics at therapeutic levels — small dose changes can cause large level changes. Always check albumin-corrected level in critically ill patients.
