Drug Action
Fosphenytoin is a pro-drug of phenytoin.
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Drug reference
Fosphenytoin is a pro-drug of phenytoin.
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Status epilepticus ▶BY INTRAVENOUS INFUSION ▶Adult: Initially 20 mg(PE)/kg, dose to be administered at a rate of 100–150 mg(PE)/minute, then 4–5 mg (PE)/kg daily in 1–2 divided doses, dose to be administered at a rate of 50–100 mg(PE)/minute, dose to be adjusted according to response and trough plasma-phenytoin concentration ▶Elderly: Consider 10–25% reduction in dose or infusion rate Prophylaxis or treatment of seizures associated with neurosurgery or head injury ▶BY INTRAMUSCULAR INJECTION, OR BY INTRAVENOUS INFUSION ▶Adult: Initially 10–15 mg(PE)/kg, intravenous infusion to be administered at a rate of 50–100 mg(PE)/minute, then 4–5 mg(PE)/kg daily in 1–2 divided doses, intravenous infusion to be administered at a rate of 50–100 mg(PE)/minute, dose to be adjusted according to response and trough plasma-phenytoin concentration ▶Elderly: Consider 10–25% reduction in dose or infusion rate Temporary substitution for oral phenytoin ▶BY INTRAMUSCULAR INJECTION, OR BY INTRAVENOUS INFUSION ▶Adult: Same dose and same dosing frequency as oral phenytoin therapy, intravenous infusion to be administered at a rate of 50–100 mg(PE)/minute ▶Elderly: Consider 10–25% reduction in dose or infusion rate DOSE EQUIVALENCE AND CONVERSION ▶Doses are expressed as phenytoin sodium equivalent (PE); fosphenytoin sodium 1.5 mg : phenytoin sodium 1 mg. l UNLICENSED USE Fosphenytoin sodium doses in BNF may differ from those in product literature.
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Acute porphyrias p. 1120. second- degree heart block. sino-atrial block. sinus bradycardia. Stokes-Adams syndrome. third-degree heart block
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Heart failure. hypotension. injection solutions alkaline (irritant to tissues). respiratory depression. resuscitation facilities must be available
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Cross-sensitivity reported with carbamazepine.
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HLA-B* 1502 allele in individuals of Han Chinese or Thai origin—avoid unless essential (increased risk of Stevens-Johnson syndrome).
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Prescriptions for fosphenytoin sodium should state the dose in terms of phenytoin sodium equivalent (PE); fosphenytoin sodium 1.5 mg : phenytoin sodium 1 mg.
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→Appendix 1: antiepileptics
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▶Common or very common Asthenia. chills. dizziness. drowsiness. dry mouth. dysarthria. euphoric mood. headache. hypotension. movement disorders. nausea. nystagmus. sensation abnormal. skin reactions. stupor. taste altered. tinnitus. tremor. vasodilation. vertigo. vision disorders. vomiting ▶Uncommon Cardiac arrest. confusion. hearing impairment . muscle complaints. muscle weakness. nervousness. oral disorders. reflexes abnormal. severe cutaneous adverse reactions (SCARs). systemic lupus erythematosus (SLE). thinking abnormal ▶Frequency not known Acute psychosis. agranulocytosis. appetite disorder. atrial conduction depression (more common if injection too rapid). atrioventricular block. bone disorders. bone fracture. bone marrow disorders. bradycardia. cardiotoxicity. cerebrovascular insufficiency. circulatory collapse (more common if injection too rapid). coarsening of the facial features. constipation. delirium. Dupuytren’s contracture. encephalopathy. granulocytopenia. groin tingling. hair changes. hepatic disorders. hyperglycaemia. hypersensitivity. insomnia. leucopenia. lymphadenopathy. nephritis tubulointerstitial. Peyronie’s disease. polyarteritis nodosa . polyarthritis. purple glove syndrome. respiratory disorders. sensory peripheral polyneuropathy. thrombocytopenia. tonic seizure. ventricular conduction depression (more common if injection too rapid). ventricular fibrillation (more common if injection too rapid) SIDE-EFFECTS, FURTHER INFORMATION Fosphenytoin has been associated with severe cardiovascular reactions including asystole, ventricular fibrillation, and cardiac arrest. Hypotension, bradycardia, and heart block have also been reported. The following are recommended: monitor heart rate, blood pressure, and respiratory function for duration of infusion; observe patient for at least 30 minutes after infusion; if hypotension occurs, reduce infusion rate or discontinue; reduce dose or infusion rate in elderly, and in renal or hepatic impairment.
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See also Pregnancy in Epilepsy p. 321. Monitoring Changes in plasma-protein binding make interpretation of plasma-phenytoin concentrations difficult—monitor unbound fraction. The dose should be monitored carefully during pregnancy and after birth, and adjustments made on a clinical basis.
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Small amounts present in milk, but not known to be harmful.
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Manufacturer advises caution— monitor free plasma-phenytoin concentration (rather than total plasma-phenytoin concentration) in hepatic impairment or hypoalbuminaemia and in hyperbilirubinaemia. Dose adjustments Manufacturer advises consider a 10–25% reduction in dose or infusion rate (except in the treatment of status epilepticus) in hepatic impairment or hypoalbuminaemia.
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Dose adjustments Consider 10–25% reduction in dose or infusion rate (except initial dose for status epilepticus).
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▶Manufacturer recommends blood counts (but evidence of practical value uncertain). ▶With intravenous use Monitor heart rate, blood pressure, ECG, and respiratory function for during infusion.
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For intermittent intravenous infusion (Pro-Epanutin ®), give in Glucose 5% or Sodium chloride 0.9%; dilute to a concentration of 1.5–25 mg (phenytoin sodium equivalent (PE))/mL.
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There can be variation in the licensing of different medicines containing the same drug. Solution for injection ELECTROLYTES: May contain Phosphate ▶Pro-Epanutin (Pfizer Ltd) Fosphenytoin sodium 75 mg per 1 ml Pro-Epanutin 750mg/10ml concentrate for solution for injection vials | 10 vial P £400.00 Nervous system (Hospital only)
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Initially 20 mg(PE)/kg, dose to be administered
First-line fragment. Read the complete Indications and Dose section above.
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Initially 10–15 mg(PE)/kg, intravenous infusion
First-line fragment. Read the complete Indications and Dose section above.
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Same dose and same dosing frequency as oral
First-line fragment. Read the complete Indications and Dose section above.
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