Nurses Compass
Drug Guide
Mephenytoin
Classification
Therapeutic: Anticonvulsant
Pharmacological: Hydantoin derivative
FDA Approved Indications
- Partial seizures
- Generalized seizures
Mechanism of Action
Mephenytoin stabilizes neuronal membranes by blocking voltage-dependent sodium channels, reducing neuronal excitability and seizure activity.
Dosage and Administration
Adult: Initial dose: 50-100 mg three times daily, titrated up as needed. Maintenance dose varies.
Pediatric: Dosing based on weight or age; initial: 2-4 mg/kg/day divided into multiple doses.
Geriatric: Start at lower doses due to increased sensitivity and decreased hepatic function.
Renal Impairment: Use caution; dose adjustments may be necessary.
Hepatic Impairment: Use with caution; possibly reduce dose due to hepatic metabolism.
Pharmacokinetics
Absorption: Well absorbed from gastrointestinal tract.
Distribution: Widely distributed; crosses blood-brain barrier.
Metabolism: Primarily hepatic via hydroxylation and conjugation processes.
Excretion: Urinary excretion of metabolites; minimal unchanged drug.
Half Life: Approximately 8-20 hours, varies among individuals.
Contraindications
- Hypersensitivity to Mephenytoin or hydantoin derivatives.
- Porphyria.
Precautions
- Monitor for hypersensitivity reactions, severe skin reactions, blood dyscrasias, gingival hyperplasia, osteomalacia.
- Use cautiously in hepatic impairment, cardiac disease, or psychosis.
- Pregnancy Category C: Risks vs. benefits should be considered; potential teratogenicity.
Adverse Reactions - Common
- Gastrointestinal upset (Rare)
- Gingival hyperplasia (Less common)
- Dizziness, drowsiness (Common)
Adverse Reactions - Serious
- Stevens-Johnson syndrome and toxic epidermal necrolysis (Rare)
- Blood dyscrasias (agranulocytosis, aplastic anemia) (Rare)
- SLE-like syndrome (Rare)
Drug-Drug Interactions
- CNS depressants, warfarin, oral contraceptives, other hepatic enzyme inducers or inhibitors.
Drug-Food Interactions
N/ADrug-Herb Interactions
N/ANursing Implications
Assessment: Baseline liver function tests, complete blood count, neurological status, gingival condition.
Diagnoses:
- Risk of bleeding (if blood dyscrasias occur)
- Risk for infection
- Altered tissue perfusion
Implementation: Administer with food to reduce gastrointestinal upset. Monitor blood levels if available. Regular dental checkups.
Evaluation: Assessment of seizure control, side effects, and appropriate blood levels if indicated.
Patient/Family Teaching
- Take medication exactly as prescribed.
- Report any skin rashes, sore throat, fever, or unusual bleeding.
- Maintain good oral hygiene to prevent gingival hyperplasia.
- Regular follow-ups for blood tests and dental health.
Special Considerations
Black Box Warnings:
- Serious dermatologic reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis).
Genetic Factors: Genetic polymorphisms in CYP enzymes may affect metabolism and toxicity.
Lab Test Interference: Can interfere with certain laboratory assays, including serum amylase and urinary metabolites.
Overdose Management
Signs/Symptoms: Drowsiness, nystagmus, ataxia, coma.
Treatment: Supportive care, activated charcoal if ingestion is recent, and symptomatic treatment. Hemodialysis is generally ineffective.
Storage and Handling
Storage: Store at room temperature, away from moisture and light.
Stability: Stable under recommended storage conditions.