A 75-year-old patient with a history of congestive heart fai…

A 75-year-old patient with a history of congestive heart failure, COPD, and stage 3 chronic kidney disease is receiving intravenous vancomycin for methicillin-resistant staphylococcus aureus (MRSA) bacteremia. The nurse knows that vancomycin can cause serious side effects. Which of the following should the nurse prioritize monitoring during vancomycin therapy for this patient?