【藥品性質提示】 根據 2019 AGS Beers Criteria，本藥品為【潛在不適當用藥 (PIM)】，不建議老年人併用 TMP/SMX 使用。

Seizure (Treatment and Prophylaxis); Generalized Tonic-Clonic and Complex Partial Seizures

Phenytoin is an antiepileptic drug that possibly enhances sodium efflux from neurons of the motor cortex. This cellular event tends to stabilize the threshold against hyperexcitability that results from excessive stimulation or environmental changes capable of reducing membrane sodium gradient. Posttetanic potentiation at synapses is then reduced preventing cortical seizure foci from detonating adjacent cortical areas.

Absorption:
Bioavailability: 20% to 90%
Distribution:
1. Protein binding: highly bound
2. Vd: 0.5 to 1.0 L/kg
Metabolism:
1. Hepatic; hydroxylation
2. Elimination Half Life: 14 hr to 22 hr
Excretion:
1. Renal: excreted in urine after reabsorbtion from intestinal tract
2. Dialyzable: Yes (hemodialysis), 41.3% ; No (peritoneal)

History of hypersensitivity to phenytoin, any component of the product, or to other hydantoins
History of prior acute hepatotoxicity attributable to phenytoin
Concomitant use with delavirdine
Concomitant use with rilpivirine

Fetal risk cannot be ruled out

Infant risk cannot be ruled out

Common:
Morbilliform eruption, Rash, Constipation, Gingival enlargement, Nausea, Vomiting, Ataxia, Nystagmus, Slurred speech, Confusion
Serious:
Lupus erythematosus, Stevens-Johnson syndrome, Toxic epidermal necrolysis, Agranulocytosis, Aplastic anemia, Granulocytopenic disorder, Leukopenia, Myelosuppression, Pancytopenia, Thrombocytopenia, Hepatotoxicity, Toxic hepatitis, Anaphylaxis, Anticonvulsant hypersensitivity syndrome, Systemic lupus erythematosus, Suicidal thoughts, Nephrotoxicity, Drug withdrawal seizure

Usual maintenance dose 300 to 400 mg/day; MAX dose 600 mg/day

Seizure, During and following neurosurgery:
5 mg/kg/day orally divided equally into 2 or 3 doses to a subsequent maximum of 300 mg/day; usual maintenance dose is 4 to 8 mg/kg/day; children over the age of 6 years may require minimum adult dose (300 mg/day)
Generalized Tonic-Clonic and Complex Partial Seizures:
5 mg/kg/day divided equally into 2 or 3 doses to a subsequent maximum of 300 mg/day; usual maintenance dose is 4 to 8 mg/kg/day; children over the age of 6 years may require minimum adult dose (300 mg/day)

No specific adjustment is necessary.

There are no dosage adjustments provided in the manufacturer's labeling; undergoes hepatic metabolism and clearance may be decreased. Monitor free phenytoin levels closely.