A nurse is caring for a client who is taking phenytoin and has a seizure disorder. For which of the following adverse effects should the nurse monitor the client?

A. Hypoglycemia: Phenytoin does not typically lower blood glucose levels, so hypoglycemia is not a common adverse effect. Blood glucose monitoring is not routinely required for clients on phenytoin unless they have an underlying metabolic disorder. B. Gingival hyperplasia: Phenytoin can cause overgrowth of gum tissue, particularly with long-term use, leading to swelling, bleeding, and discomfort. Good oral hygiene and regular dental care are important to manage and prevent progression. This is a well-documented and common adverse effect of the medication. C. Ringing of the ears: Tinnitus is more commonly associated with high doses of certain antibiotics or salicylates, not phenytoin. Although phenytoin toxicity can cause neurologic symptoms, ringing in the ears is not a primary concern for routine monitoring. D. Elevated blood pressure: Phenytoin does not directly raise blood pressure. Blood pressure monitoring is still important for overall health, but hypertension is not an expected adverse effect of this anticonvulsant medication.