Parenteral Manual

Fosphenytoin

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Alternate Name(s): 
CEREBYX
Classification: 
Anticonvulsant
Original Date: 
June 2011
Revised Date: 
April 2014
Indications: 
  • Treatment of convulsive status epilepticus
  • Short term parenteral replacement for oral phenytoin
Reconstitution and Stability: 

**** Dose, concentration and infusion rates are expressed as phenytoin sodium equivalents (PE)

****Fosphenytoin should always be prescribed and dispensed in mg of phenytoin equivalents (PE)

  • Available as PE 50 mg/mL
  • Store vials in refrigerator.  Vials stable 48 hours at room temperature
  • Stable in D5W or NS at concentration of 1-20 mg/mL 30 days room temperature or refrigerated

 

Compatibility: 

-Solutions Compatible:  D5W, D10W, NS, D5W/0.45NaCl, D5RL, RL

-Additive/Above Cassette Compatible:  KCL

-Y-site Compatible:  Lorazepam

-Incompatible:  Midazolam

Administration: 

(For approved routes of administration by nursing personnel, refer to Policy for the Administration of Intravenous Medications.)

SC NO
IM YES.  Not for status epilepticus
IV Direct

YES.  Not recommended. Cardiac monitoring.  BP monitoring
Max Infusion rate:  3 mg PE/kg/min
to a max of 150 mg PE/min
IV Intermittent Infusion

YES
Usual dilution:  for doses less than 100 mg:  5 mg PE/mL
-for doses greater than or equal to 100 mg :  20 mg PE/mL
Infusion time:  10 to 30 minutes
Max Infusion rate:  3 mg PE/kg/min to a max of 150 mg PE/min
IV Continuous Infusion NO
Dosage: 

(For neonatal dosages, refer to Neonatal IV Drug Manual.)

**** Dose, concentration and infusion rates are expressed as phenytoin sodium equivalents (PE)

****Fosphenytoin should always be prescribed and dispensed in mg of phenytoin equivalents (PE)

Children:

-Status epilepticus:

  • Loading:  20 mg PE/kg IV in a single or divided dose (maximun 1 gram PE)
  • Maintenance (anticonvulsant) : usually starts 12 hours after loading dose
    -0.5 - 3 yrs:  8 - 10 mg PE/kg/day in 2-3 divided doses
    -4 - 6 yrs:  7.5 - 9 mg PE/kg/day in 2-3 divided doses
    -7 - 9 yrs:  7 - 8 mg PE/kg/day in 2-3 divided doses
    -10 - 16 yrs:  6 - 7 mg PE/kg/day in 2-3 divided doses
    - greater than 16 yrs:  4 - 6 mg PE/kg/day in 2 - 3 divided doses

Adults:

-Status epilepticus:

  • Loading:  20 mg PE/kg IV (maximum 1 gram PE)
  • Initial maintenance:  4 - 6 mg PE/kg IM/IV in 2-3 divided doses

IV substitution for oral phenytoin -  use the same total daily PE dose as fosphenytoin.
Plasma concentrations may increase slightly with this method.  Monitor clinical response and phenytoin concentration to further guide dose adjustments after 3 - 4 days.

Potential hazards of parenteral administration: 
  • Hypotension, vasodilation, respiratory depression, tachycardia, bradycardia, arrhythmia (with rapid IV administration)
  • Burning, pruritus, tingling, parethesia (with doses greater than or equal to 15 mg/kg and fast infusion rates)
  • Rash, dermatitis, facial edema
Notes: 
  • Monitor blood pressure and ECG with IV loading doses
  • Monitor serum phenytoin concentrations.  Measure serum phenytoin 2 hours after IV load or 4 hours after IM injection
  • Monitor liver enzymes
  • Each 1 mg of PE contains 0.0037 mmol of phosphate
  • Not an irritant and does not need an antidote in the event of extravasation

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