Which symptom is least likely to be observed in a patient with phenytoin toxicity?

• A. Slurred speech
• B. Coma
• C. Hepatic encephalopathy
• D. Nystagmus

Answer: (C)

In cases of phenytoin toxicity, the symptoms typically observed are not indicative of hepatic encephalopathy. Phenytoin, an anticonvulsant, can lead to a range of neurological symptoms primarily because of its effects on the central nervous system. Common signs of toxicity include slurred speech, coma, and nystagmus—these reflect direct impacts on motor coordination and neurological functioning.

Hepatic encephalopathy, however, is a condition resulting from severe liver dysfunction and is characterized by a series of symptoms related to the accumulation of toxins in the brain, primarily due to liver failure. While one might see neurological disturbances in both hepatic encephalopathy and phenytoin toxicity, the occurrence of hepatic encephalopathy is specifically linked to liver impairment rather than pharmacological toxicity from phenytoin itself. Thus, it is least likely to be present in a patient experiencing phenytoin toxicity compared to the other symptoms mentioned, which are more directly correlated with its effects on the nervous system.