An older adult client is receiving vancomycin for a hospital acquired infection (HAI). Which intervention is most important for the nurse to implement?

A. Obtain a white blood count daily to determine response of infection: Changes in WBC may lag behind clinical improvement and do not prevent toxicity. While useful, it is not the most critical intervention for preventing adverse effects of vancomycin. B. Report the acquired infection to the Medicare reimbursement office: Reporting HAIs is important for facility tracking and reimbursement policies, but this is an administrative task. It does not address the immediate clinical priority of ensuring safe and effective vancomycin therapy. C. Ensure that vancomycin peak and trough levels are prescribed: Monitoring peak and trough levels is essential to maintain therapeutic efficacy while preventing nephrotoxicity and ototoxicity, which are significant risks in older adults. D. Assess the older adult client's physiological response to the antibiotic: Observing clinical response is important, but without drug level monitoring, the nurse cannot ensure that the antibiotic is both safe and effective. Clinical changes alone may not reveal early signs of toxicity.