A patient on gentamicin for two weeks develops a renal condition with significantly decreased glomerular filtration rate. What dosage adjustment is appropriate?

• A. The drug should be discontinued.
• B. The dosage should be increased.
• C. The time interval between dosages should be increased.
• D. No dosage adjustment is required.

Answer: (C)

Gentamicin is cleared by the kidneys, so a significant drop in glomerular filtration rate reduces how quickly the drug is eliminated. If you keep giving the same dose at the same interval, the drug can accumulate, raising trough levels and increasing the risk of further nephrotoxicity and ototoxicity. The best adjustment is to increase the time interval between doses, giving more time for elimination before the next dose and lowering trough concentrations while still allowing a therapeutic peak. In practice, dosing intervals are adjusted based on creatinine clearance and often coupled with trough level monitoring to ensure safety. Increasing the interval minimizes accumulation; increasing the dose would worsen toxicity; not adjusting would allow ongoing accumulation; stopping therapy could be necessary if toxicity progresses, but extending the interval is the correct approach to continue treatment safely.