Phenobarbital, Serum
Use
Phenobarbital is used as a central nervous system suppressant to control generalized and partial seizures. It is often coadministered with other drugs for complex seizure disorders. Monitoring the therapeutic concentration of phenobarbital is crucial to ensure efficacy while preventing toxicity. It is particularly useful in assessing patient compliance with medication regimens or detecting possible overdose scenarios, as toxicity can lead to sedation, reduced respiratory function, and potentially life-threatening situations.
Special Instructions
Phenobarbital is absorbed slowly but completely, with significant bioavailability. Doses range from 60 to 300 mg/day in adults or 3 to 6 mg/kg/day in children. Patients must coordinate the timing of sample collection to match steady-state blood levels, which are adjusted after two weeks of therapy based on observed blood concentrations.
Limitations
The test is effective in tracking phenobarbital levels, but it does not account for drug interactions affecting other medications metabolized through the hepatic cytochrome P450 pathway. Acute intermittent porphyria might be induced by phenobarbital, leading to attacks due to stimulation of the cytochrome P450 system. Typical cautionary measures should be observed if incompatible specimen types are submitted, as they may cause the specimen to be rejected.
FDA ApprovedNew York Approved
Methodology
Other
Biomarkers
LOINC Codes
- 3948-7
- 3948-7
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
Plastic vial
Collection Instructions
Serum gel tubes should be centrifuged within 2 hours of collection. Red-top tubes should be centrifuged, and the serum aliquoted into a plastic vial within 2 hours of collection.
Causes for Rejection
Gross hemolysis
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 72 hours |
| Refrigerated | 7 days |
| Frozen | 28 days |