Phenobarbital, Serum or Plasma
Also known as: Luminal®, Phenobarbital Level, Blood
Use
Phenobarbital, a long-acting barbiturate, is effective in generalized tonic-clonic and simple partial seizures. Higher plasma concentrations may be required to control the latter. Complex partial seizures do not respond as well, and absence seizures are not relieved and may be exacerbated. Phenobarbital frequently is used in the treatment of neonatal seizures and may be the initial drug employed in young children; however, because of increasing concern about adverse neuropsychological reactions to sedative/hypnotic antiepileptic drugs, many neurologists prefer less sedating drugs, such as carbamazepine, phenytoin, or valproate. The prophylactic use of phenobarbital in infants with febrile seizures has been challenged. Phenobarbital also is useful in seizures caused by barbiturate withdrawal in dependent individuals. The sodium salt is administered parenterally as part of the treatment regimen for status epilepticus.
Special Instructions
Phenobarbital has a half-life of 84 to 108 hours and can affect the metabolism of drugs like phenytoin, ethosuximide, and various others, increasing their clearance and elimination. Clinical monitoring through laboratory assessments is recommended when these drugs are used concurrently with phenobarbital.
Limitations
The use of gel-barrier tubes is not recommended due to slow absorption of the drug by the gel, potentially affecting drug level measurement. Depending on volume and storage conditions, drug absorption into the gel can be clinically significant. Patients on phenobarbital should be monitored due to its interaction with various drugs that can affect clearance and elimination. Furthermore, its effectiveness can vary among different seizure types.
Methodology
Immunoassay
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
1 mL
Minimum Volume
0.3 mL
Container
Red-top tube or green-top (heparin) tube. Do not use a gel-barrier tube.
Collection Instructions
Transfer separated serum to a plastic transport tube. Peak: 4 to 12 hours after dose; trough: immediately prior to next dose.
Storage Instructions
Room temperature
Causes for Rejection
Gel-barrier tube; hemolysis; severe lipemia; icteric specimen
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 14 days |
| Refrigerated | 14 days |
| Frozen | 14 days |
