Which of the following is NOT a symptom of phenytoin overdose?

• A. Nystagmus
• B. Ataxia
• C. Diplopia
• D. Rash

Answer: (D)

Phenytoin overdose mainly causes central nervous system toxicity that shows up as ocular and motor disturbances. Nystagmus occurs early because the excess drug disrupts cerebellar and vestibular function, leading to involuntary eye movements. Ataxia follows as coordination breaks down and gait becomes unsteady. Diplopia, or double vision, results from impaired extraocular muscle control due to CNS depression. These features reflect the neurotoxic effects of too much phenytoin.

Rash is not part of the typical acute overdose syndrome. While phenytoin can cause skin reactions in some patients during therapy, this sign does not indicate overdose and is not driven by the same CNS depressant mechanism seen with excessive levels. If a rash develops, it warrants evaluation for a hypersensitivity reaction or other causes, but it isn’t a marker of phenytoin overdose like the neurological signs are.