Table 1

Summary of clinical and biochemical signs of phenytoin toxicity

Clinical signs of toxicity
Organ system involvedManifestations
Cerebellum
  • Nystagmus

  • Ataxia

  • Slurred speech

  • Cerebellar atrophy

Central nervous system
  • Behavioural changes

  • Increased seizure activity (hypocalcaemia induced)

  • Lethargy and confusion

  • Coma

Cutaneous/mucocutaneous
  • Maculopapular exanthema

  • Hirsutism

  • Toxic epidermal necrolysis

  • Stevens-Johnson syndrome

  • Erythroderma

  • Leukocytoclastic vasculitis

  • Fixed drug eruptions

  • Angioedema

  • Pseudolymphoma

  • Gingival hypertrophy

Endocrine system
  • Hypothyroidism

  • Decreased bone mineral density

  • Rickets/osteomalacia

  • Male hyposexuality and sperm dysmotility

Gastrointestinal system
  • Ageusia

  • Nausea

  • Dysphagia

  • Heartburn

  • Constipation

  • Diarrhoea

Biochemical signs of toxicity
  • Megaloblastic anaemia

  • Aplastic anaemia

  • Elevated ALT, AST, ALP

  • Hypocalcaemia

  • Altered TFT

  • Hyperglycaemia

  • Increased SHBG

  • ALP, alkaline phosphatase; ALT, alanine transaminase; AST, aspartate transaminase; SHBG, sex hormone binding globulin; TFT, thyroid function test.