A nurse is caring for a client who is receiving gentamicin. Which of the following findings indicates the client is developing toxicity?

A. Lethargy: Lethargy can be a nonspecific symptom of many conditions, including infection or general illness, but it is not a hallmark sign of gentamicin toxicity. While monitoring overall status is important, lethargy alone does not indicate ototoxicity or nephrotoxicity. B. Weight gain: Weight gain may reflect fluid retention or other metabolic changes, but it is not a primary indicator of gentamicin toxicity. Nephrotoxicity could eventually cause fluid retention, but weight gain is a delayed and nonspecific finding. C. Tinnitus: Tinnitus, or ringing in the ears, is a classic early sign of ototoxicity associated with aminoglycosides like gentamicin. It indicates damage to the inner ear and requires immediate assessment and potential discontinuation of the drug to prevent permanent hearing loss. D. Slurred vision: Slurred vision is not typically associated with gentamicin toxicity. Visual changes are not a known adverse effect of aminoglycosides, so this finding would prompt evaluation for other causes rather than drug toxicity.