The nurse is caring for a client who is receiving gentamicin IV. Which adverse effect is most important for the nurse to report to the healthcare provider (HCP)?

A. Nausea: Nausea is a relatively common and nonspecific adverse effect that may occur with many medications, including antibiotics. While it can affect comfort and oral intake, it is generally not considered a severe or life-threatening complication. It does not represent the most critical toxicity associated with gentamicin. B. Oliguria: Oliguria, defined as decreased urine output, is a critical finding when a client is receiving gentamicin because it may indicate developing nephrotoxicity. Aminoglycosides accumulate in renal tubular cells and can cause acute tubular necrosis, leading to impaired kidney function. Early recognition of reduced urine output allows prompt evaluation of renal function, potential discontinuation of the drug, and prevention of permanent kidney damage. C. Vertigo: Vertigo can occur with gentamicin due to ototoxicity, particularly involving the vestibular portion of the eighth cranial nerve. Although this is a serious adverse effect that requires reporting, renal impairment generally takes priority because it can rapidly progress to acute kidney injury and significantly affect drug clearance. D. Headache: Headache is a nonspecific symptom that may occur from multiple causes, including stress, dehydration, or minor medication effects. It is not a hallmark toxicity associated with aminoglycoside therapy. Compared with complications such as nephrotoxicity or ototoxicity, headache does not represent a high-priority adverse effect requiring urgent reporting.