No Difference in Response to Nitrofurantoin with Reduced Kidney Function

Mild to moderate reductions in kidney function don’t alter the treatment failure rate of nitrofurantoin in older women with urinary tract infections, concludes a report in the Canadian Medical Association Journal.

Using Ontario health databases, the researchers identified a cohort of 9223 older women with reduced kidney function receiving one of four oral antibiotics commonly used for reduced urinary tract infections: nitrofurantoin, ciprofloxacin, norfloxacin, or trimethoprim/sulfamethoxazole (TMP-SMX). The women’s median age was 79 years and median estimated glomerular filtration rate (eGFR) 38 mL/min/1.73 m2.

Fourteen-day treatment failure rates were examined in terms of need for a second antibiotic or hospital encounter for urinary tract infection. The same outcomes were assessed in a cohort of 182,634 women with relatively high eGFR: median 69 mL/min/1.73 m2.

Women receiving the four antibiotics had similar baseline characteristics. Among those with low eGFR, failure rates were significantly higher with nitrofurantoin compared to ciprofloxacin and norfloxacin (but not TMP-SMX).

However, analysis of the cohort with relatively high eGFR revealed a similar pattern of higher treatment failure rates with nitrofurantoin. Compared to nitrofurantoin, adjusted odds ratios for a second prescription with ciprofloxacin were 0.43 for women with lower kidney function and 0.50 for those with higher kidney function.

Previous reports have suggested subtherapeutic concentrations of nitrofurantoin in patients with reduced kidney function, leading to the suggestion that this antibiotic be avoided when the eGFR is less than 40 mL/min/1.73 m2. The new analysis finds no increase in the nitrofurantoin failure rate in older women with mild to moderate reductions in kidney function. Regardless of eGFR, treatment failure is more likely with nitrofurantoin than with other antibiotic choices [Singh N, et al: Kidney function and the use of nitrofurantoin to treat urinary tract infections in older women. CMAJ 2015. DOI:10.1503/cmaj.150067].