What is nitrofurantoin typically used for and what renal function parameter must be adequate?

• A. Uncomplicated urinary tract infections; creatinine clearance generally >60 mL/min.
• B. Pyelonephritis; creatinine clearance >30 mL/min.
• C. Prophylaxis of traveler's diarrhea; creatinine clearance >20 mL/min.
• D. Broad-spectrum infections; any renal function acceptable.

Answer: (A)

Nitrofurantoin works best for uncomplicated lower urinary tract infections because it is excreted into the urine and achieves very high concentrations in the bladder, where it can effectively eradicate typical pathogens of cystitis. It is not reliable for infections above the bladder, such as pyelonephritis, or for systemic infections, since it does not consistently reach effective serum or renal tissue levels needed to treat those sites.

Renal function matters because nitrofurantoin is predominantly eliminated by the kidneys. Adequate renal function allows the drug to be concentrated in the urine at levels that can treat a bladder infection. The usual threshold used is creatinine clearance greater than about 60 mL/min. When clearance is lower, urinary concentrations drop, reducing efficacy and increasing the risk of treatment failure. Therefore, the best answer is: used for uncomplicated lower UTIs, with creatinine clearance generally greater than 60 mL/min.