Phenytoin (Dilantin) Loading Dose in Dialysis Patients
The loading dose of phenytoin for dialysis patients is the same as for patients with normal renal function: 15-20 mg/kg IV (or 10-15 mg/kg in adults), administered at a rate not exceeding 50 mg/min in adults or 1-3 mg/kg/min in pediatric patients, with no supplemental dose needed after dialysis. 1
Standard Loading Dose Applies Regardless of Dialysis Status
Phenytoin loading doses do not require adjustment for renal impairment or dialysis status because the drug is primarily hepatically metabolized and minimally removed by hemodialysis 1, 2
For status epilepticus in adults: administer 10-15 mg/kg IV at a rate not exceeding 50 mg per minute 1
For status epilepticus in pediatric patients: administer 15-20 mg/kg IV at a rate not exceeding 1-3 mg/kg/min or 50 mg per minute, whichever is slower 1
For non-emergent loading in adults: use 10-15 mg/kg IV with the same rate restrictions 1
Why Dialysis Doesn't Change the Loading Dose
Hemodialysis removes only 2-4% of an intravenous phenytoin dose, with dialysis clearance of only 7-14 ml/min compared to plasma clearance of 53-133 ml/min 2
No supplemental dose is necessary after hemodialysis because the contribution of dialysis to phenytoin removal is negligible 2
The half-life of phenytoin in uremic patients (11-18 hours) is not significantly shortened by hemodialysis 2
Critical Monitoring Considerations in Dialysis Patients
Monitor unbound (free) phenytoin concentrations rather than total concentrations in dialysis patients, as protein binding is significantly decreased in uremia 1, 3
Free phenytoin concentrations are elevated in predialysis serum compared to postdialysis serum due to uremic compounds that interfere with protein binding 3
Therapeutic effect occurs with total serum concentrations of 10-20 mcg/mL (unbound concentrations of 1-2 mcg/mL), but in dialysis patients, focus on the unbound fraction 1
The fraction of unbound phenytoin is increased in patients with renal disease and hypoalbuminemia, making unbound level monitoring more clinically relevant 1
Administration Guidelines
Continuous monitoring of ECG, blood pressure, and respiratory function is essential during IV administration 1
Follow the loading dose with maintenance doses of 100 mg orally or IV every 6-8 hours 1
Do not administer intramuscularly for acute treatment, as peak serum levels may require up to 24 hours to achieve 1
Common Pitfall to Avoid
Do not reduce the loading dose based on renal function or dialysis status - this is the most critical error to avoid, as underdosing will result in subtherapeutic levels and inadequate seizure control 1, 2
Do not give supplemental doses after dialysis sessions, as this leads to unnecessary drug accumulation 2