|Trade names||Cerebyx, others|
|Other names||Fosphenytoin sodium|
|Main uses||Status epilepticus, prevent seizures|
|Side effects||Dizziness, nystagmus, itchiness, numbness, sleepiness, poor coordination|
|Elimination half-life||15 minutes to convert to phenytoin|
|Excretion||Kidney (as phenytoin)|
|Chemical and physical data|
|Molar mass||362.278 g·mol−1|
|3D model (JSmol)|
Fosphenytoin, sold under the brand name Cerebyx among others, is a medication used to treat status epilepticus and prevent seizures. It may be used instead of phenytoin in those who cannot take medication by mouth. It is given by injection into a vein or muscle.
Common side effects include dizziness, nystagmus, itchiness, numbness, sleepiness, and poor coordination. Other side effects may include low blood pressure, QT prolongation, Stevens-Johnson syndrome, angioedema, and liver problems. Use in pregnancy may harm the baby. It is a prodrug of phenytoin and works by blocking sodium channels.
Fosphenytoin was approved for medical use in the United States in 1996. It is available as a generic medication. In the United Kingdom a 750 mg vial costs the NHS about £40. In the United States this amount costs about 24 USD.
Fosphenytoin is approved in the United States for the short-term (five days or fewer) treatment of epilepsy when more widely used means of phenytoin administration are not possible or are ill-advised, such as endotracheal intubation, status epilepticus or some other type of repeated seizures; cluster seizure ,vomiting, and the person is unalert or not awake or both.
To determine PE 150 mg of fosphenytoin is equivalent to 100 mg of phenytoin.
Side effects are similar to intravenous phenytoin and include hypotension, cardiac arrhythmias, CNS adverse events (nystagmus, dizziness, sedation/somnolence, ataxia and stupor), and local dermatological reactions. Purple glove syndrome probably occurs with fosphenytoin but possibly at lower frequency than with intravenous phenytoin. Fosphenytoin can cause hyperphosphatemia in end-stage renal failure patients.
One millimole of phenytoin is produced for every millimole of fosphenytoin administered; the hydrolysis of fosphenytoin also yields phosphate and formaldehyde, the latter of which is subsequently metabolized to formate, which is in turn metabolized by a folate dependent mechanism.
Phenytoin, in both its acidic and sodium salt forms, is erratically bioavailable whether it is injected or taken orally due to its high melting point, weak acidity, and its being only sparingly soluble in water. Simply putting patients on other drugs is not always an option; this was especially true before 1993, when the number of anticonvulsants available was much more limited. One solution was to develop a prodrug that did not have these drawbacks.
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