Antibiotic Commonly Used for UTI Less Effective Than Others

Veronica Hackethal, MD

April 28, 2015

Older women treated with nitrofurantoin for urinary tract infection (UTI) had higher rates of treatment failure than those who received other first-line antibiotics, according to a study by Namisha Singh, from the Division of Nephrology, Department of Medicine, Western University, London, Ontario, Canada, and colleagues, published online April 27 in the Canadian Medical Association Journal.

"In our setting, nitrofurantoin was the most commonly prescribed antibiotic for a urinary tract infection in older women irrespective of their kidney function," lead author Amit Garg, MD, PhD, commented in a press release. Dr Garg is a nephrologist in the Department of Medicine, Western University.

"These patients had more treatment failures with nitrofurantoin compared with other antibiotics, such as ciprofloxacin. However, this was evident regardless of a patient's level of kidney function," he added.

Worldwide, physicians write about 25 million prescriptions for nitrofurantoin annually. The antibiotic, primarily eliminated via glomerular filtration, can become subtherapeutic in patients with reduced renal function. With age, estimated glomerular filtration (eGFR) declines, leaving more than 25% of adults aged 65 years and older with decreased kidney function. Although recommendations advise against prescribing nitrofurantoin in patients with reduced renal function, this practice remains controversial because of weak supporting evidence.

The population-based, retrospective cohort study took place from June 2002 to March 2013 and included women with a mean age of 79 years or older in Ontario, Canada. The researchers used six linked healthcare databases to obtain patient information. Included patients had a relatively low eGFR (median, 38 mL/minute per 1.73 m2; n = 9223) or a relatively high eGFR (median, 69 mL/minute per 1.73 m2; n = 182,634).Women had been prescribed one of the following commonly used first-line antibiotics for uncomplicated UTIs: nitrofurantoin, ciprofloxacin, norfloxacin, or trimethoprim-sulfamethoxazole.

Women with both low and high eGFRs most commonly received nitrofurantoin (40.5% and 38.7%, respectively).

Women with low eGFRs who received ciprofloxacin had lower likelihood of needing a second antibiotic (130 [6.5%] of 1989 vs 516 [13.8%] of 3739; odds ratio [OR], 0.44, 95% confidence interval [CI], 0.36 - 0.53) or visiting the hospital (21 [1.1%] of 1989 vs 95 of 3739 [2.5%]; OR, 0.41; 95% CI, 0.25 - 0.66) compared with those who received nitrofurantoin.

Women who received norfloxacin had similar rates of treatment failure (second antibiotic: 6.5% vs 13.8%; OR, 0.44; 95% CI, 0.36 - 0.53; hospital visit: 1.2% vs 2.5%; OR, 0.46; 95% CI, 0.29 - 0.72). Similar but nonsignificant results occurred with trimethoprim-sulfamethoxazole.

Results in women with relatively high eGFRs paralleled those with low eGFRs.

These associations remained after adjustment for 11 potential confounders. In subanalyses of women with low, medium, and high renal function and with available baseline serum creatinine values, those who received ciprofloxacin or norfloxacin had lower likelihood of needing a second antibiotic than did the nitrofurantoin group.

Because women with low and high eGFRs experienced similar rates of treatment failure with nitrofurantoin, the authors suggest physicians may not need to avoid its use in patients with decreased renal function. Rather, basing these decisions on factors such as local bacterial resistance could become an option. This approach could take some pressure off physicians to prescribe fluoroquinolones, for which bacterial resistance remains a concern.

Dr Garg reports grants from Astellas and Roche, and his institution has unrestricted research funding from Pfizer. The other authors have disclosed no relevant financial relationships.

CMAJ. Published online April 27, 2015. Abstract

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