The nurse is caring for a client prescribed phenytoin who is admitted to the hospital. Which assessment finding is most concerning?

A. The client has a lack of muscle coordination: Phenytoin can cause ataxia or mild coordination issues, particularly at higher therapeutic levels. While concerning, these are often dose-related and typically manageable with monitoring and dose adjustment. B. The client's gums are red and swollen: Gingival hyperplasia is a common, non-life-threatening adverse effect of chronic phenytoin use. It requires dental hygiene management but is not acutely dangerous. C. The client has yellowing of the sclera: Jaundice indicates potential hepatotoxicity or liver dysfunction, a serious and potentially life-threatening complication of phenytoin therapy. Liver impairment can affect drug metabolism and overall health, making this the most concerning finding. D. The client is falling asleep in their bed: Drowsiness is a common CNS effect of phenytoin, particularly during initiation or dose escalation. While it requires monitoring for safety, it is not immediately life-threatening.