A client taking phenytoin develops new neurologic symptoms. Which cluster is most consistent with phenytoin toxicity?
1Nystagmus, ataxia, slurred speech, and confusion✓ Correct answer
2Pinpoint pupils, respiratory depression, and constipation
3Severe diarrhea, abdominal cramping, and flushing
4Tinnitus, rapid breathing, diaphoresis, and fever
Explanation
Dose-related phenytoin neurotoxicity can cause nystagmus, ataxia, slurred speech, decreased coordination, somnolence, and confusion. The other clusters are more consistent with opioid toxicity, a gastrointestinal reaction, or salicylate toxicity. The nurse should hold further doses if directed by the medication parameters, protect the client from falls, and promptly notify the prescriber for clinical and serum-level evaluation.
Clinical reasoning Phenytoin toxicity primarily produces dose-related neurologic findings such as nystagmus, ataxia, dysarthria, impaired coordination, somnolence, and confusion.
Decision rule Recognize the neurologic cluster, institute safety precautions, and escalate for medication review and serum-concentration assessment.
Scenario 45-year-old male on phenytoin 300 mg PO daily × 6 weeks. Trough serum level today: 24 mcg/mL (therapeutic range 10-20). He reports the room "feels wobbly."
Phenytoin neurotoxicity — Dose-related central nervous system toxicity that can cause nystagmus, ataxia, slurred speech, somnolence, and confusion.
Nystagmus — Involuntary rhythmic eye movement that can be an early sign of dose-related phenytoin toxicity.
Narrow therapeutic index — A small margin between therapeutic and toxic doses; phenytoin requires regular level monitoring.