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Phenytoin
Test CodePTN
Alias/See Also
Dilantin, Diphenylhydantoin, PTN
Preferred Specimen
1.0 mL plasma (0.5 mL minimum)
Instructions
Collect specimen two (2) hours after completion of IV loading dose and eight (8) hours after oral loading dose.
Trough: collect immediately before dose (within thirty [30] minutes)
Trough: collect immediately before dose (within thirty [30] minutes)
Transport Container
PST (light green top). Red top and SST also acceptable
Specimen Stability
Room temperature: 24 hours, Refrigerated: 2 days, Frozen: 5 months
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Grossly hemolyzed specimens are unacceptable.
Reference Range
Therapeutic: 10.0 - 20.0 ug/mL
Clinical Significance
"Phenytoin is an anti-epileptic drug. Test results are used in the diagnosis and treatment of phenytoin overdose and in monitoring levels of phenytoin to ensure appropriate therapy.
Phenytoin is widely used and effective for all types of seizure disorders except absence seizures. It is of value in the treatment of elementary partial (focal) or complex partial epilepsy (psychomotor, temporal lobe) seizures, but ineffective in petit mal epilepsy. Occasionally, it is used in the treatment of cardiac arrhythmias.
Because of considerable inter-individual variation and the limited capacity for the liver to metabolize phenytoin, blood concentrations should be monitored to obtain maximal anti-seizure effect. Once metabolism is saturated, small dosage changes may result in disproportionate changes in blood concentration and can cause wide variations in dosage requirements among patients."
Phenytoin is widely used and effective for all types of seizure disorders except absence seizures. It is of value in the treatment of elementary partial (focal) or complex partial epilepsy (psychomotor, temporal lobe) seizures, but ineffective in petit mal epilepsy. Occasionally, it is used in the treatment of cardiac arrhythmias.
Because of considerable inter-individual variation and the limited capacity for the liver to metabolize phenytoin, blood concentrations should be monitored to obtain maximal anti-seizure effect. Once metabolism is saturated, small dosage changes may result in disproportionate changes in blood concentration and can cause wide variations in dosage requirements among patients."
