An 82-year-old hospitalized patient with creatinine clearance of 25 mL/min has a microbial infection requiring treatment with antibiotics. Which one of the following drugs is least likely to require a dosage adjustment, either a smaller dose than usual or an increased interval between doses?

Erythromycin is eliminated largely via biliary excretion and decreases in renal function do not usually require a dosage reduction unless creatinine clearance <10mL/min. All of the other antimicrobial drugs listed are eliminated by the kidney, at rates proportional to creatinine clearance, so major dose reductions would be needed in patients with renal dysfunction to avoid toxicity.