Intramuscular fosphenytoin (Cerebyx®) in patients requiring a loading dose of phenytoin

R. E. Ramsay, B. J. Wilder, B. M. Uthman, W. R. Garnett, J. M. Pellock, G. L. Barkley, I. E. Leppik, L. E. Knapp

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Fosphenytoin (Cerebyx®), is a water soluble prodrug that is rapidly and completely converted to phenytoin. This study reports the injection-site tolerance and safety of intramuscular fosphenytoin (> 10 mg/kg doses) in 60 patients requiring a phenytoin loading dose. Patients received injections at single or multiple sites with volumes ranging from 4 to 30 ml per injection site. The majority of patients had no irritation (erythema, swelling, tenderness, bruising) or complaints of discomfort related to fosphenytoin injection either after injection (95%) or at follow-up (88%). Irritation, when reported, was mild in all cases. Forty of 60 patients (67%) reported transient side effects, primarily involving the central nervous system, such as nystagmus, dizziness or ataxia, which are commonly associated with phenytoin therapy. All patients received prescribed doses; no patient had an injection(s) stopped due to intolerance or side effects. No serious adverse events occurred with intramuscular fosphenytoin. In this study, intramuscular fosphenytoin was demonstrated to be a safe and well tolerated, and in many instances, a preferable alternative to other means of phenytoin loading.

Original languageEnglish (US)
Pages (from-to)181-187
Number of pages7
JournalEpilepsy Research
Issue number3
StatePublished - Jan 1 1997



  • Fosphenytoin
  • Injection site irritation
  • Phenytoin
  • Prodrugs
  • Routes of administration

Cite this

Ramsay, R. E., Wilder, B. J., Uthman, B. M., Garnett, W. R., Pellock, J. M., Barkley, G. L., Leppik, I. E., & Knapp, L. E. (1997). Intramuscular fosphenytoin (Cerebyx®) in patients requiring a loading dose of phenytoin. Epilepsy Research, 28(3), 181-187.