Skip to content
ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Phenytoin prodrug (anticonvulsant)

Fosphenytoin sodium

Brand names: Pro-Epanutin

Fosphenytoin sodium is a water-soluble phenytoin prodrug given by injection for status epilepticus and as a short-term parenteral substitute for oral phenytoin.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

It is rapidly converted to phenytoin, which blocks voltage-gated sodium channels to stabilise neuronal membranes and limit the spread of seizure activity.

Prescribing in practice

  • Doses are prescribed in phenytoin sodium equivalents to avoid dosing errors, and rapid administration can cause severe hypotension and cardiac arrhythmias requiring cardiac and blood-pressure monitoring.
  • It carries the risk of serious skin reactions and hepatotoxicity, and exhibits non-linear (saturable) pharmacokinetics shared with phenytoin.
  • Severe cardiovascular reactions are more likely in elderly or seriously ill patients, so the infusion rate must be controlled.

Monitoring

Continuous ECG, blood pressure and respiratory monitoring are required during and after infusion, with phenytoin plasma concentrations checked once conversion is complete.

Counselling the patient

  • This medicine will be given and monitored in hospital with heart-rhythm and blood-pressure observation.
  • The care team should report any rash, fever or yellowing of the skin promptly.
  • Tell staff about all other medicines, as interactions are common.

Evidence & guidelines

Fosphenytoin is an established parenteral option in status epilepticus and offers better infusion-site tolerability than intravenous phenytoin.

Reference: NICE NG217; UK status epilepticus algorithms; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Pathways