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Pronunciation |
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(me
FEN i
toyn) |
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U.S. Brand
Names |
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Mesantoin® |
|
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Generic
Available |
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No |
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Synonyms |
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Methoin; Methylphenylethylhydantoin; Phenantoin |
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Pharmacological Index |
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Anticonvulsant, Hydantoin |
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|
Use |
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Treatment of tonic-clonic and partial seizures in patients who are
uncontrolled with less toxic anticonvulsants; usually used in combination with
other anticonvulsants |
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Pregnancy Risk
Factor |
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C |
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Contraindications |
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Hypersensitivity to mephenytoin, other hydantoins, or any
component |
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Adverse
Reactions |
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>10%:
Central nervous system: Psychiatric changes, slurred speech, trembling,
dizziness, drowsiness
Gastrointestinal: Constipation, nausea, vomiting
1% to 10%:
Central nervous system: Headache, insomnia
Dermatologic: Skin rash
Gastrointestinal: Anorexia, weight loss
Hematologic: Leukopenia
Hepatic: Hepatitis
Renal: Increase in serum creatinine |
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Drug
Interactions |
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CYP2C19 enzyme substrate
Increased effect/toxicity with alcohol, sulfonamides, chloramphenicol,
cimetidine, isoniazid, disulfiram, phenothiazines, benzodiazepines
|
|
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Mechanism of
Action |
|
Stabilizes neuronal membranes and decreases seizure activity by increasing
efflux or decreasing influx of sodium ions across cell membranes in the motor
cortex during generation of nerve impulses; prolongs effective refractory period
and suppresses ventricular pacemaker automaticity, shortens action potential in
the heart |
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|
Usual Dosage |
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Oral:
Adults: Initial dose: 50-100 mg/day given daily; increase by 50-100 mg at
weekly intervals; usual maintenance dose: 200-600 mg/day in 3 divided doses;
maximum: 800 mg/day |
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|
Dietary
Considerations |
|
Alcohol: Additive CNS depression; has been reported with hydantoins; avoid or
limit alcohol
Food:
Fresh fruits containing Vitamin C: Displaces drug from binding sites,
resulting in increased urinary excretion of hydantoin; education patients
regarding the potential for decreased anticonvulsant effect of hydantoins with
consumption of foods high in Vitamin C
Glucose: Hyperglycemia and glycosuria may occur in patients receiving
high-dose therapy; monitor blood glucose concentration, especially in patients
with impaired renal function |
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Mental Health: Effects
on Mental Status |
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Drowsiness and dizziness are common; may cause insomnia; may rarely cause
confusion |
|
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Mental Health:
Effects on Psychiatric
Treatment |
|
May cause leukopenia; use caution with clozapine or carbamazepine; may induce
hepatic enzymes; caution with concurrent psychotropics; monitor for altered
response |
|
|
Dental Health: Local
Anesthetic/Vasoconstrictor
Precautions |
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No information available to require special precautions |
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Dental Health:
Effects on Dental Treatment |
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Mephenytoin, like phenytoin, causes gingival hyperplasia. Usually starts
during the first 6 months of dental treatment as gingivitis. The incidence is
higher in patients under 20 years of age. To minimize severity and growth rate
of gingival tissue begin a program of professional cleaning and patient plaque
control within 10 days of starting anticonvulsant therapy. GH induced by
mephenytoin disappears with cessation of drug therapy. |
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|
Patient
Information |
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Take with food, avoid alcoholic beverages; may cause dizziness, drowsiness,
and impair coordination or judgment |
|
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Nursing
Implications |
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Monitor CBC and platelet |
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Dosage Forms |
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Tablet: 100 mg |
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