Fosphenytoin as Phenytoin, Serum or Plasma
Use
This test is used to measure serum or plasma phenytoin (Dilantin) levels in patients, including those receiving fosphenytoin, to assess whether therapeutic levels (typically 10–20 µg/mL total, 1–2 µg/mL free) have been achieved. It supports management of seizure disorders and arrhythmias and is used to guide dosing adjustments while ensuring safe, effective drug concentrations.
Special Instructions
When monitoring phenytoin levels in patients treated with fosphenytoin, avoid drawing the specimen until at least 2 hours after completion of an IV fosphenytoin infusion or at least 4 hours after an IM dose to minimize analytical interference that may lead to falsely elevated phenytoin levels.
Limitations
Use of immunoanalytical assays like fluorescence polarization or enzyme-multiplied immunoassay may cross-react with fosphenytoin, particularly if samples are collected too soon after fosphenytoin administration, causing overestimation of phenytoin concentration. Clinicians should interpret elevated phenytoin levels with caution if sampling is premature relative to fosphenytoin dosing.
Methodology
Immunoassay
Biomarkers
Result Turnaround Time
Not provided.
Related Documents
For more information, please review the documents below
Specimen
Serum
Volume
Not provided
Minimum Volume
Not provided
Other tests from different labs that may be relevant