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FPHNY
PHENYTOIN (DILANTIN®), FREE, SERUM

Test Code FPHNY 
Test PHENYTOIN (DILANTIN®), FREE, SERUM 
Methodology Immunoassay 
Description Phenytoin is the drug of choice to treat and prevent tonic-clonic and psychomotor seizures. If phenytoin alone will not prevent seizure activity, co-administration with phenobarbital is usually effective. 
Specimen Draw blood in a plain, red-top tube. Spin down and send 2.0 mL (minimum volume: 1.0 mL) of serum refrigerated.

NOTE:
1. Due to phenytoin's long elimination half-life, the actual sampling time is unimportant. However, when making comparative measurements, it is important that the sampling time be consistent. For therapeutic studies, collect within 1 hour prior to the next dose.
2. When using fosphenytoin, it is recommended that phenytoin concentrations not be monitored until conversion of fosphenytoin to phenytoin is essentially complete. This occurs within approximately 2 hours after the end of IV infusion and 4 hours after IM injection. Serum phenytoin concentrations measured before this conversion is complete will not be accurate. 

Reference Values Therapeutic concentration: 1.2 - 2.5 µg.mL
Toxic concentration: > 4.0 µg/mL 
Analytic Time 1 Day - AVAILABLE STAT 
Day(s) Test Set Up Monday through Sunday 
CPT Code(s) 80186