Raw research findings for this medication. Mostly single studies, not curated or confirmed robust.
Fosphenytoin is a water-soluble prodrug of phenytoin, given by injection or drip, that the body converts to phenytoin within minutes. It is gentler on veins than phenytoin injection and is used to stop prolonged seizures (status epilepticus), to prevent seizures during brain surgery, and when phenytoin cannot be taken by mouth. It is sold as Cerebyx, among other names.
Because fosphenytoin becomes phenytoin, the same two genes matter. CYP2C9 breaks phenytoin down, and people with reduced-function versions such as *2 and *3 clear it more slowly, so levels can rise high. HLA-B*15:02, most common in parts of East and South-East Asia, is linked to rare severe skin reactions. CPIC has published a guideline on both genes covering fosphenytoin, and the US FDA lists them.
Clinical guidelines that name a gene for Cerebyx. They sort people into groups by the gene copies they carry.
US FDA: HLA-B. *15:02 positive. Data that Support Therapeutic Management Recommendations.
More drugs from the same category
Antiepileptics (class) (Anticonvulsants)
Not a prescribing recommendation. This page is educational information about pharmacogenomic research and clinical guidelines - it is not medical or dosing advice, and not a prediction of how any medication will work for you. Never start, stop, or change a medication or dose based on it; talk to your doctor or pharmacist, who can order clinical-grade testing if appropriate.
Content updated September 2026.
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