Phenytoin, Total and Phenobarbital Group, Serum
Use
This test is useful for monitoring the therapeutic concentration of phenytoin and phenobarbital in the serum to ensure appropriate medication dosage, assess compliance, and detect potential drug toxicity. Phenytoin is commonly prescribed to treat tonic-clonic and psychomotor seizures, while phenobarbital acts as a CNS suppressant that aids in managing generalized and partial seizures. Both drugs are frequently coadministered to control complex seizure disorders. Monitoring these levels helps prevent toxicity associated with small increases in dosage, which can significantly affect blood concentrations.
Special Instructions
Not provided.
Limitations
The pharmacokinetics of phenytoin are affected by coadministered drugs such as phenobarbital and valproic acid, which can alter absorption, protein binding, and clearance rate. Phenytoin does not follow classical half-life kinetics as its clearance rate varies with drug concentration. Phenobarbital's effects also vary due to its enzyme-induction properties, necessitating careful dosage management to maintain therapeutic levels while avoiding toxicity. Usage may induce acute intermittent porphyria.
FDA ApprovedNew York Approved
Methodology
Immunoassay (Kinetic Interaction of Microparticles in a Solution (KIMS))
Biomarkers
LOINC Codes
- 104596-2 - Phenytoin & Phenobarbital pnl Ser
- 3948-7 - Phenobarb SerPl-mCnc
- 3968-5 - Phenytoin SerPl-mCnc
Result Turnaround Time
1 day
Related Documents
For more information, please review the documents below
Specimen
Serum
Volume
0.5 mL
Minimum Volume
0.25 mL
Container
Red top or serum gel; aliquot to plastic vial
Collection Instructions
Centrifuge and aliquot serum into a plastic vial within 2 hours of collection.
Storage Instructions
Refrigerated preferred.
Causes for Rejection
Gross hemolysis will lead to rejection.
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 72 hours |
| Refrigerated | 14 days |
| Frozen | 28 days |