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phenytoin (fen-i-toyn)

Dilantin, Phenytek


Therapeutic: antiarrhythmics (group IB), anticonvulsants

Pharmacologic: hydantoins


Treatment/prevention of tonic-clonic (grand mal) seizures and complex partial seizures. Unlabeled Use: As an antiarrhythmic, particularly for ventricular arrhythmias associated with digoxin toxicity, prolonged QT interval, and surgical repair of congenital heart diseases in children. Management of neuropathic pain, including trigeminal neuralgia.


Limits seizure propagation by altering ion transport. May also decrease synaptic transmission. Antiarrhythmic properties as a result of shortening the action potential and ↓ automaticity. Therapeutic Effects: Diminished seizure activity. Termination of ventricular arrhythmias.

Adverse Reactions/Side Effects

Most listed are for chronic use of phenytoin

CNS: ataxia, agitation, confusion, dizziness, drowsiness, dysarthria, dyskinesia, extrapyramidal syndrome, headache, insomnia, weakness. EENT: diplopia, nystagmus. CV: hypotension (↑ with IV phenytoin), tachycardia. GI: gingival hyperplasia, nausea, constipation, drug-induced hepatitis, vomiting. Derm: hypertrichosis, rash, exfoliative dermatitis, pruritus. Hemat: AGRANULOCYTOSIS, APLASTIC ANEMIA, leukopenia, megaloblastic anemia, thrombocytopenia. MS: osteomalacia. Misc: ALLERGIC REACTIONS, INCLUDING STEVENS-JOHNSON SYNDROME, fever, lymphadenopathy.


Examination and Evaluation

  • Be alert for phenytoin hypersensitivity syndrome (fever, skin rash, lymphadenopathy). Rash usually occurs within the first 2 wk of therapy. Hypersensitivity syndrome usually occurs at 3–8 wk but may occur up to 12 wk after initiation of therapy. Report these signs immediately because this syndrome may lead to renal failure, rhabdomyolysis, or hepatic necrosis.

  • Monitor other skin reactions (itching/burning skin, hives, exfoliation, dermatitis). Notify physician immediately about because certain skin reactions may indicate serious hypersensitivity reactions (Stevens-Johnson syndrome).

  • Be alert for signs of agranulocytosis (fever, sore throat, mucosal lesions, signs of infection), aplastic anemia (unusual fatigue, weakness, dizziness, pallor), thrombocytopenia (bruising, nose bleeds, bleeding gums), or fatigue and poor health that might be due to other anemias and blood dyscrasias. Report these signs to the physician immediately. Periodic blood tests may be needed to monitor WBC and RBC counts.

  • Document the number, duration, and severity of seizures to help determine if this drug is effective in reducing seizure activity.

  • Assess dizziness that might affect gait, balance, and other functional activities (See Appendix C). Report balance problems and functional limitations to the physician and nursing staff, and caution the patient and family/caregivers to guard against falls and trauma.

  • Monitor daytime drowsiness, confusion, or agitation. Repeated or excessive symptoms may require change in dose or medication.

  • Assess gait and motor function and document any signs of incoordination, ataxia, or other motor symptoms that might indicate extrapyramidal syndrome such as involuntary movements of the jaw, limbs, Parkinson-like symptoms, and other dystonias and dyskinesias. Report these signs to the physician.

  • If treating neuropathic pain, use visual analogue scales and other appropriate pain scales to assess the patient's pain and help ...

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