In a patient treated for UTI with piperacillin-tazobactam and gentamicin, what step helps prevent nephrotoxicity?

• A. Increase hydration
• B. Measure plasma gentamicin levels
• C. Switch to fluoroquinolone
• D. Monitor urine output

Answer: (B)

Aminoglycosides like gentamicin can cause damage to the renal tubules because they are cleared by the kidneys and have a narrow therapeutic window. The most direct way to prevent nephrotoxicity while still using this antibiotic is to monitor the drug’s exposure in the bloodstream. By measuring plasma gentamicin levels (typically trough levels before the next dose, and sometimes peak levels), you can tailor the dose or extend the dosing interval to keep drug concentrations within a safe range. This approach directly limits the renal exposure that drives toxicity.

Hydration helps support kidney function, but it doesn’t specifically control how much gentamicin is getting into the renally exposed tissues. Monitoring urine output is important for detecting evolving nephrotoxicity, not for preventing it. Switching to a different antibiotic avoids the risk, but may not be appropriate if the current regimen is needed to treat the infection and dosing can be adjusted safely.