Brands, Medical Use, Clinical Data
- Capsule (extended release)
Brands / Synonyms
5,5-Dwufenylohydantoina; 5,5-Dwufenylohydantoina [Polish]; Aleviatin; Antisacer; Auranile; Causoin; Cerebyx; Citrullamon; Citrulliamon; Comital; Comitoina; Convul; Danten; Dantinal; Dantoinal; Dantoinal klinos; Dantoine; Denyl; Di-Hydan; Di-Lan; Di-Lan (VAN); Di-Phetine; Didan TDC 250; Didan-tdc-250; Difenilhidantoina; Difenilhidantoina (spanish); Difenilhidantoina [Spanish]; Difenin; Difetoin; Difhydan; Dihycon; Dihydantoin; Dilabid; Dilantin; Dilantin acid; Dilantin Kapseals; Dilantin-125; Dilantine; Dillantin; Dintoin; Dintoina; Diphantoin; Diphedal; Diphedan; Diphenat; Diphenin; Diphenine; Diphentoin; Diphentyn; Diphenylan; Diphenylan Sodium; Diphenylhydantoin; Diphenylhydantoin (VAN); Diphenylhydantoine; Diphenylhydantoine [French]; Diphenylhydatanoin; Ditoinate; DPH; DPH (VAN); Ekko; Ekko capsules; Elepsindon; Enkelfel; Epamin; Epanutin; Epasmir "5"; Epasmir 5; Epdantoin Simple; Epdantoine simple; Epelin; Epifenyl; Epihydan; Epilan; Epilan D; Epilan-D; Epilantin; Epinat; Epised; Eptal; Eptoin; Extended Phenytoin Sodium; Fenantoin; Fenantoin Mn Pharma; Fenidantoin "s"; Fenidantoin s; Fenitoina; Fenitoina [INN-Spanish]; Fentoin; Fenylepsin; Fenytoin Dak; Fenytoine; Fosphenytoin; Gerot-epilan-D; Hidan; Hidantal; Hidantilo; Hidantina; Hidantina senosian; Hidantina vitoria; Hidantomin; Hindatal; Hydantal; Hydantin; Hydantoin; Hydantoinal; Hydantol; Ictalis simple; Idantoil; Idantoin; Iphenylhydantoin; Kessodanten; Labopal; Lehydan; Lepitoin; Lepsin; Mesantoin; Minetoin; Neos-Hidantoina; Neosidantoina; Novantoina; Novophenytoin; Om hidantoina simple; Om-Hydantoine; Oxylan; Phanantin; Phanatine; Phenatine; Phenatoine; Phenhydan; Phenhydanin; Phenitoin; Phentoin; Phentytoin; Phenytek; Phenytex; Phenytoin; Phenytoin AWD; Phenytoin Base; Phenytoin Sodium; Phenytoin USP; Phenytoin-Gerot; Phenytoine; Phenytoine [INN-French]; Phenytoinum [INN-Latin]; Prompt Phenytoin Sodium; Ritmenal; Saceril; Sanepil; Silantin; Sinergina; Sodanthon; Sodantoin; Sodanton; Solantin; Solantoin; Solantyl; Sylantoic; Tacosal; Thilophenyl; TOIN; Toin unicelles; Zentronal; Zentropil
For the control of generalized tonic-clonic (grand mal) and complex partial (psychomotor, temporal lobe) seizures and prevention and treatment of seizures occurring during or following neurosurgery.
Phenytoin is an antiepileptic drug which can be useful in the treatment of epilepsy. The primary site of action appears to be the motor cortex where spread of seizure activity is inhibited. Phenytoin reduces the maximal activity of brain stem centers responsible for the tonic phase of tonic-clonic (grand mal) seizures. Phenytoin acts to damp the unwanted, runaway brain activity seen in seizure by reducing electrical conductance among brain cells. It lacks the sedation effects associated with phenobarbital. There are some indications that phenytoin has other effects, including anxiety control and mood stabilization, although it has never been approved for those purposes by the FDA.
Mechanism of Action
Phenytoin acts on sodium channels on the neuronal cell membrane, limiting the spread of seizure activity and reducing seizure propagation. By promoting sodium efflux from neurons, phenytoin tends to stabilize the threshold against hyperexcitability caused by excessive stimulation or environmental changes capable of reducing membrane sodium gradient. This includes the reduction of post-tetanic potentiation at synapses. Loss of post-tetanic potentiation prevents cortical seizure foci from detonating adjacent cortical areas.
Bioavailability 70-100% oral, 24.4% for rectal and intravenous administration. Rapid rate of absorption with peak blood concentration expected in 1½ to 3 hours.
Oral, mouse: LD50 = 150 mg/kg; Oral, rat: LD50 = 1635 mg/kg. Symptoms of overdose include coma, difficulty in pronouncing words correctly, involuntary eye movement, lack of muscle coordination, low blood pressure, nausea, sluggishness, slurred speech, tremors, and vomiting.
Biotrnasformation / Drug Metabolism
Phenytoin is contraindicated in those patients who are hypersensitive to phenytoin or other hydantoins.
There are many drugs which may increase or decrease phenytoin levels or which phenytoin may affect. Serum level
determinations for phenytoin are especially helpful when possible drug interactions are suspected. The most commonly
occurring drug interactions are listed below:
1. Drugs which may increase phenytoin serum levels include: acute alcohol intake, amiodarone,
chloramphenicol, chlordiazepoxide, diazepam, dicumarol, disulfiram, estrogens, H2-antagonists, halothane,
isoniazid, methylphenidate, phenothiazines, phenylbutazone, salicylates, succinimides, sulfonamides, tolbutamide,
2. Drugs which may decrease phenytoin serum levels include: carbamazepine, chronic alcohol abuse,
reserpine, and sucralfate. Moban brand of Molindone Hydrochloride contains calcium ions which interfere with the
absorption of phenytoin. Ingestion times of phenytoin and antacid preparations containing calcium should be staggered
in patients with low serum phenytoin levels to prevent absorption problems.
3. Drugs which may either increase or decrease phenytoin serum levels include: phenobarbital, sodium
valproate, and valproic acid. Similarly, the effect of phenytoin on phenobarbital, valproic acid and sodium valproate
serum levels is unpredictable.
4. Although not a true drug interaction, tricyclic antidepressants may precipitate seizures in susceptible
patients and phenytoin dosage may need to be adjusted.
5. Drugs whose efficacy is impaired by phenytoin include: corticosteroids, coumarin anticoagulants,
digitoxin, doxycycline, estrogens, furosemide, oral contraceptives, quinidine, rifampin, theophylline, vitamin D.
Drug/Laboratory Test Interactions
Phenytoin may cause decreased serum levels of protein-bound iodine (PBI). It may also produce lower than normal
values for dexamethasone or metyrapone tests. Phenytoin may cause increased serum levels of glucose, alkaline
phosphatase, and gamma glutamyl transpeptidase (GGT).