Phenytoin

Nursing pharmacology study reference (NCLEX-style monograph). Numeric values are standard teaching ranges for study and must be verified against current manufacturer labeling before clinical use. This is educational content, not prescribing guidance.

Phenytoin (brand name Dilantin) — Anticonvulsant; Hydantoin (sodium channel blocker) (NTI).

Identification

• Therapeutic class: Anticonvulsant.
• Pharmacologic class: Hydantoin (sodium channel blocker) (NTI).

Pharmacology

• Mechanism of action: Stabilizes neuronal membranes by blocking sodium channels, limiting seizure spread.
• Onset / peak / duration: PO variable; IV onset within minutes; duration dose dependent.
• Half-life / therapeutic level: Half-life about 22 hours (nonlinear); therapeutic level 10 to 20 mcg/mL (free 1 to 2 mcg/mL).

Clinical use

• Indications: Tonic-clonic and focal seizures, status epilepticus (IV).
• Usual dose, route, frequency: Loading then 100 mg PO three times daily or extended once daily; IV per protocol.
• Maximum dose / adjustments: IV no faster than 50 mg/min (25 mg/min in elderly); adjust to free level in low albumin or renal disease.

Safety

• Contraindications: Sinus bradycardia, heart block, hypersensitivity.
• Black box warning: None formal; IV rate-related cardiotoxicity (hypotension, arrhythmia) requires slow administration and cardiac monitoring.
• Interactions: Many CYP interactions, warfarin, oral contraceptives (reduced effect), enteral feeds (reduce absorption, hold feeds around dosing), alcohol.
• Pregnancy / lactation: Teratogenic; use only if essential.
• High-alert: No.

Adverse effects

• Common side effects: Gingival hyperplasia, nystagmus, ataxia, hirsutism, rash.
• Serious effects to report: Stevens-Johnson syndrome, blood dyscrasias, hepatotoxicity, purple glove syndrome (IV).
• Antidote / reversal: None; supportive care.

Nursing process

• Assessment before administration: Seizure baseline, drug level, CBC, albumin, oral and gum status.
• Interventions during therapy: Use only normal saline for IV (precipitates in dextrose); flush line; hold tube feeds around oral dosing.
• Monitor: Drug level, CBC, LFTs, gum health, seizure frequency.
• Evaluation / expected outcome: Seizure control within the therapeutic range.

Patient teaching

• Patient teaching: Brush and floss to protect gums; do not switch brands; use backup contraception.
• Notify provider if: Rash, fever, sore throat, easy bruising, persistent dizziness.
• Administration tips: Same brand; IV in saline only and slow; separate from tube feeds.