The nurse reviews laboratory results for a client with a traumatic brain injury prescribed phenytoin. The nurse notes the phenytoin level is 32 mg/dL (normal range 10-20 mg/dL). Which findings should the nurse anticipate? Select all that apply.

This case involves phenytoin toxicity resulting from a level exceeding the therapeutic range of 10 to 20 mg/dL. Knowledge of central nervous system effects, pharmacokinetics, and toxicological manifestations of anticonvulsants is necessary to identify appropriate neurological assessment findings. Choice A rationale Nystagmus, or involuntary eye movement, is a classic sign of phenytoin toxicity as levels rise above 20 mg/dL. It results from the drug's effect on the cerebellum and vestibular system, disrupting normal extraocular muscle coordination and balance. Choice B rationale Phenytoin typically causes hyperglycemia rather than hypoglycemia because it inhibits insulin secretion. A serum level of 32 mg/dL would not be expected to lower blood glucose; monitoring for elevated glucose levels is more appropriate in toxicity. Choice C rationale Ataxia involves uncoordinated muscle movements and gait instability, frequently occurring when phenytoin levels exceed therapeutic limits. The drug affects cerebellar function, leading to significant motor impairment and increasing the client's risk for falls and physical injury. Choice D rationale Vertigo or dizziness is a common central nervous system side effect of high phenytoin concentrations. As the drug reaches toxic levels like 32 mg/dL, it interferes with vestibular signaling, causing the sensation of spinning or loss of balance. Choice E rationale Phenytoin toxicity is more likely to cause blood dyscrasias like leukopenia or thrombocytopenia rather than a high platelet level. Normal platelet counts are 150,000 to 400,000 cells/mm; high levels are not a recognized manifestation of phenytoin overdose.