Measuring oxygen saturation is not directly relevant to the administration of vancomycin or the monitoring of its potential side effects. While oxygen saturation is important to assess in patients with respiratory concerns, it does not provide information about kidney function, which is essential for safe vancomycin use.

Choice B rationale:

Auscultating bowel sounds, while a part of general abdominal assessment, is not the most crucial action before administering vancomycin. Vancomycin is not known to have significant effects on bowel motility, and its primary concern is nephrotoxicity.

Choice C rationale:

Assessing body temperature can be helpful in evaluating for infection, but it is not the most specific or sensitive indicator of vancomycin-related adverse effects. Fever can be a sign of various conditions, and it does not directly assess kidney function.

Choice D rationale:

Checking serum creatinine is the most essential action before administering vancomycin because it allows for assessment of kidney function. Vancomycin is primarily excreted by the kidneys, and impaired renal function can lead to elevated drug levels and increased risk of nephrotoxicity. By checking serum creatinine, the nurse can ensure that the patient's kidney function is adequate to safely excrete vancomycin and can adjust the dosage or frequency of administration if necessary.