A male client has been receiving the antibiotic gentamicin sulfate IV piggyback every 12 hours for several days. Which observations by the nurse indicate that the client may be experiencing an adverse effect of gentamicin?

Gentamicin sulfate is an aminoglycoside antibiotic that can cause ototoxicity, which is damage to the inner ear leading to hearing loss or balance problems. Therefore, a decrease in hearing is an indication that the client may be experiencing an adverse effect of gentamicin. Option b, decreased blood urea nitrogen, is not an adverse effect of gentamicin, but it may indicate improvement in kidney function, which can be a positive outcome of treatment. Option c, a white blood cell count of 6,000/mm3 (6x109/L), is within the normal range and is not necessarily an adverse effect of gentamicin. Option d, photophobia, is not a common adverse effect of gentamicin and may indicate a different condition or medication effect.