Test Details
Methodology
Immunoassay
Result Turnaround Time
Within 1 day
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
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.
References
Custom Additional Information
Phenobarbital has a half-life of 84 to 108 hours. Phenobarbital can affect the metabolism of phenytoin, ethosuximide, and increase the clearance and elimination of chloramphenicol, theophylline, oral anticoagulants (warfarin), cyclosporine, and oral contraceptives; where appropriate, the use of these drugs in patients on phenobarbital should be monitored clinically and through the laboratory.
Specimen Requirements
Specimen
Serum or plasma
Volume
1 mL
Minimum Volume
0.3 mL
Container
Red-top tube or green-top (heparin) tube. Do not use a gel-barrier tube. The use of gel-barrier tubes is not recommended due to slow absorption of the drug by the gel. Depending on the specimen volume and storage time, the decrease in drug level due to absorption may be clinically significant.
Collection Instructions
Transfer separated serum or plasma to a plastic transport tube. Peak: 4 to 12 hours after dose; trough: immediately prior to next dose.
Stability Requirements
Temperature | Period |
|---|---|
Room temperature | 14 days |
Refrigerated | 14 days |
Frozen | 14 days |
Freeze/thaw cycles | Stable x3 |
Reference Range
Therapeutic: 15−40 μg/mL
Storage Instructions
Room temperature
Causes for Rejection
Gel-barrier tube; hemolysis; severe lipemia; icteric specimen
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 007823 | Phenobarbital, Serum | 3948-7 | 007828 | Phenobarbital, Serum | ug/mL | 3948-7 |
| Order Code | 007823 | |||||
| Order Code Name | Phenobarbital, Serum | |||||
| Order Loinc | 3948-7 | |||||
| Result Code | 007828 | |||||
| Result Code Name | Phenobarbital, Serum | |||||
| UofM | ug/mL | |||||
| Result LOINC | 3948-7 |