A nurse is reinforcing teaching with a client who has a new prescription for cephalexin to treat a urinary tract infection. For which of the following adverse effects should the nurse instruct the client to monitor and report to the provider?

A. Diarrhea: Cephalexin, like other antibiotics, can disrupt normal gut flora and lead to antibiotic-associated diarrhea. Severe or persistent diarrhea may indicate a more serious condition, such as Clostridioides difficile infection, which requires prompt medical evaluation. Monitoring and reporting this symptom is important for preventing complications. B. Insomnia: Insomnia is not a common adverse effect of cephalexin. While some medications can cause sleep disturbances, cephalexin’s side-effect profile primarily involves gastrointestinal and hypersensitivity reactions rather than central nervous system effects. C. Vertigo: Vertigo is not typically associated with cephalexin therapy. Neurological symptoms are rare and usually linked to other drug classes or preexisting conditions. Persistent dizziness would require evaluation, but it is not expected with standard cephalexin use. D. Hypotension: Cephalexin does not normally cause hypotension. Blood pressure changes are uncommon unless a severe allergic reaction occurs, which would present with multiple systemic symptoms, such as rash, swelling, or difficulty breathing.