A nurse is teaching a client who has a new prescription for phenobarbital. The nurse would instruct the client to monitor for and report which side effect of this medication?

A. Anxiety: Phenobarbital is a barbiturate that depresses the central nervous system and is more likely to cause sedation than anxiety. Anxiety is not a typical side effect and would not be the primary concern for clients taking this medication. B. Diarrhea: Gastrointestinal upset can occur with some medications, but diarrhea is not a common or expected adverse effect of phenobarbital. More significant risks involve central nervous system depression and impaired alertness. C. Drowsiness: Phenobarbital acts as a sedative-hypnotic and anticonvulsant, so drowsiness and lethargy are common side effects. Excessive sedation should be reported because it may interfere with daily activities and signal the need for dosage adjustment. D. Metallic taste: Altered taste sensation, such as a metallic taste, is not associated with phenobarbital therapy. This side effect is more commonly linked to other drug classes such as antibiotics or certain antiepileptic agents, but not barbiturates.