A nurse is caring for a patient receiving gentamicin sulfate, an Aminoglycoside antibiotic, for a severe bacterial infection. Which assessment finding should the nurse report immediately to the healthcare provider?

A. Decreased urine output.: A reduction in urine output is a critical finding because gentamicin is nephrotoxic and can cause acute kidney injury by damaging renal tubule cells. Early signs of nephrotoxicity include oliguria, increased serum creatinine, and elevated BUN levels. B. Mild nausea.: Nausea is a relatively common and mild side effect of many antibiotics, including gentamicin. It does not usually indicate toxicity and can often be managed with supportive care or by adjusting administration timing. C. Slightly elevated heart rate.: A mild increase in heart rate may occur due to infection, fever, or stress, but it is not directly linked to gentamicin toxicity. The nurse should continue to monitor vital signs but prioritize assessment of renal and auditory function. D. Headache.: Headache can occur with antibiotic therapy or as a symptom of infection but is generally not an urgent finding. The primary toxicities are nephrotoxicity and ototoxicity, making renal assessment findings such as decreased urine output the highest priority.