Phenytoin

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Phenytoin

Indications

• epilepsy
  • except absence seizures
  • Used for tonic clonic and partial seizures, including complex partial seizures
• trigeminal neuralgia

Mechanism of action and pharmacology

• Use dependant blocker of Na channels

Dose

• individually adjusted
• plasma concentration measured 2/52 after treatment starting and adjusted to individuals to give serum [phenytoin] of 40-100 micromol/L

Adverse effects

• CNS: high concentrations can cause cerebellar syndrome (ataxia, nystagmus, intention tremor, dysarthria)
• Phenytoin intoxication may paradoxically cause seizures
• Haematological effects
  • macrocytic anaemia
• Foetal effects
  • increased perinatal mortality
• common
  • nausea
  • vomiting
  • mental confusion
  • dizziness
  • headache
  • tremor
  • transient nervousness
  • insomnia
• rare
  • dyskinesia
  • peripheral neuropathy
• overdosage
  • ataxia
  • slurred speech
  • nystagmus
  • blurred vision
• others
  • rashes
  • gingival hypertrophy / tenderness
  • coarse facies
  • acne
  • hirsutism
  • fever
  • hepatitis
  • Systemic Lupus Erythematosus
  • Stevens-Johnson Syndrome
  • Toxic Epidermal Necrolysis
  • Polyarteritis Nodosa
  • Lymphadenopathy
  • haematological
    • megaloblastic anaemia
    • leucopenia
    • thrombocytopenia
    • agranulocytosis
    • aplastic anaemia
  • reduction in plasma calcium
    • rickets / osteomalacia

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