Phenytoin, Serum or Plasma
Also known as: Dilantin®, Diphenylhydantoin, Phenytek®
Use
Phenytoin is useful in generalized tonic-clonic, complex partial, and simple partial seizures and frequently is chosen for initial therapy, particularly in adults. Because of phenytoin's potential adverse reactions (hirsutism, gingival hyperplasia, coarsening of facial features), other antiepileptic drugs are often prescribed for infants and young children. Phenytoin is commonly given with phenobarbital, primidone, carbamazepine, or valproate when monotherapy fails. It is ineffective in absence, myoclonic, and atonic seizures and is not recommended for the treatment of infantile spasms, Lennox-Gastaut syndrome, and epileptic syndromes in older children and adolescents when absence seizures or myoclonus is present. Intravenous phenytoin sodium is effective for status epilepticus and can be used as the initial drug to manage recurrent seizures if they are widely spaced. This drug also may prevent seizures initially in high-risk patients with head trauma. Phenytoin has been advocated for many other disorders, but conclusive evidence of effectiveness is inadequate for most proposed indications.
Special Instructions
Phenytoin should be monitored thoroughly due to its potential drug interactions and the risk of adverse effects including hirsutism, gingival hyperplasia, and coarsening of facial features. It has a potent enzyme-inducing ability that can interfere with the actions of other drugs such as cyclosporine, oral anticoagulants, and oral contraceptives.
Limitations
Phenytoin may interfere with other medications even at normal levels, necessitating careful monitoring of drug interactions. It is crucial for determining seizure control effectiveness, especially in conjunction with other antiepileptic medications. Since phenytoin is ineffective for certain types of seizures, its usage is limited to specific types of epileptic disorders, excluding conditions like absence and myoclonic seizures.
Methodology
Immunoassay
Biomarkers
LOINC Codes
- 3968-5
- 3968-5
Result Turnaround Time
1 day
Related Documents
For more information, please review the documents below
Specimen
Plasma
Volume
1 mL
Minimum Volume
0.8 mL
Container
Green-top (heparin) tube. Do not use a gel-barrier tube.
Collection Instructions
Transfer separated serum or plasma to a plastic transport tube. IV: two to four hours after loading dose. Oral: peak: three to nine hours after dose, immediately prior to next dose. Optimal resampling after change in dosage: 48 hours.
Storage Instructions
Room temperature
Causes for Rejection
Gel-barrier tube; severe hemolysis; lipemia
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 14 days |
| Refrigerated | 14 days |
| Frozen | 14 days |
