- Treatment of Phenobarbital resistant seizures
- IV intermittent infusion:over 10 - 30 minutes
- (maximum rate: 3 mg of Phenytoin Equivalents (PE)/kg/min)
- IM
*** Fosphenytoin should always be prescribed in mg of Phenytoin Equivalents (PE)
- Loading dose: 20 mg PE/kg IV/IM
- Maintenance dose: 5 - 8 mg/kg/day PE/kg/day IV/IM divided BID
* Start at lower end of dosing range and titrate upwards based on efficacy/side effects
- CVS: hypotension (with rapid IV administration), vasodilation, tachycardia, bradycardia
- Dermatologic: rash,exfoliative dermatitis
- Endocrine and metabolic: hyperglycemia
- Hematologic: neutropenia, thrombocytopenia, anemia
- Local: pain on injection (less irritation at injection site and phlebitis than with phenytoin), paresthesia, pruritis
- BP, HR
- CBC with differential, platelets
- Serum glucose
- Liver enzymes
- Therapeutic Phenytoin levels: 40 - 80 micromol/L
- Usual sampling time:
- After load: at least 2 hours after end of IV infusion or 4 hours after IM load injection
- Maintenance: trough level for IV or IM administration (0 - 60 minutes before next dose) on day 3
- Usual sampling time:
*** Dose, concentration and infusion rates are expressed as Phenytoin Equivalents (PE)
- Fosphenytoin PE 50 mg/mL
- Take 1 mL (PE 50 mg) and add to 9 mL of 0.9% NaCl
- Final concentration: PE 5 mg/mL
- Store vials in refrigerator. Vials stable 48 hours at room temperature
- Solutions Compatible: D5W, D10W, 0.9 % NaCl, dextrose-saline combinations
- Y-site Compatible: lorazepam, phenobarbital, potassium chloride
- Incompatible: calcium gluconate, midazolam, TPN
*Dose, concentration and infusion rates are expressed as Phenytoin Equivalents (PE)
Fosphenytoin 1 mg PE = Phenytoin 1 mg
IM or IV substitution for oral Phenytoin:
Initial: Use the same total daily dose in PE of Fosphenytoin. Monitor clinical response and Phenytoin serum levels to further guide dose adjustment after 3 - 4 days. Plasma concentrations may increase slightly with this method since oral phenytoin is 90% bioavailable and phenytoin derived from IM or IV Fosphenytoin is 100% bioavailable.
- Each 1 mg of PE contains 0.0037 mmol of phosphate
-Taketomo CK, Hodding JH, Kraus DM. Pediatric Dosage Handbook 17th Edition. Hudson: Lexi-Comp Inc; 2010
-Lau E. (Editor). Drug Handbook and Formulary- The Hospital for Sick Children. Toronto: 2010 - 2011