Which symptom would require immediate nursing intervention in a client taking phenytoin?

Swollen gums require immediate nursing intervention in a client taking phenytoin because this medication is known to cause gingival hyperplasia, a condition where the gum tissue overgrows and becomes swollen. This side effect can lead to complications such as difficulty in maintaining oral hygiene, increased risk of infections, and potential issues with swallowing or eating. Prompt attention to swollen gums can help manage the condition effectively and prevent further complications. Addressing this symptom can also encourage the patient to maintain proper dental care, which is essential for overall health, especially when on long-term medication like phenytoin.