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31-07-2011 | Internal medicine | Article

Cranberries not as effective as antibiotics at preventing UTIs


Free abstract

MedWire News: One year's prophylactic treatment with trimethoprim-sulfamethoxazole (TMP-SMX) is more effective than treatment with cranberry capsules at preventing urinary tract infections (UTIs), indicate study results.

The number of patients with at least one symptomatic UTI was higher in those who received 12-month cranberry treatment versus TMP-SMX for the same time-period, and the median time to first symptomatic UTI was shorter in the cranberry group.

Cranberries have been used in the prevention of UTIs for many years, explain the researchers, although their mechanism of action is not entirely understood.

However, the alternative therapy, low-dose antibiotic prophylaxis, could lead to drug resistance, and as such, has "stimulated interest in novel nonantibiotic methods for the prevention of UTIs," write Suzanne Geerlings (Academic Medical Center, Amsterdam, the Netherlands) and colleagues in the Archives of Internal Medicine.

The team conducted their investigation into the efficacy of cranberry extract at preventing UTI in a cohort of 221 premenopausal women with a medical history of the condition.

The women were randomly assigned to receive either 12 months treatment with 480 mg TMP-SMX (n=110), or 500 mg cranberry extract in capsule form for the same duration (n=111).

After a year of treatment, the mean number of symptomatic UTIs experienced by the women was 1.8 in those treated with TMP-SMX and 4.0 in those treated with cranberry extract. The corresponding proportions of patients with at least one symptomatic UTI during the year was 71.1% and 78.2%.

TMP-SMX patients had a median time to UTI recurrence of 8 months, compared with 4 months for cranberry-treated patients.

Of note, after 1 month of TMP-SMX treatment, the researchers found that resistance to TMP-SMX, TMP, and amoxicillin had increased from 21.1-27.8% to 72.5-90.5% in both fecal and urine samples. All patients' resistance levels returned to baseline at 3 months after treatment discontinuation.

There was no increase in antibiotic resistance among cranberry-treated women.

No significant differences in adverse event rates were noted between the treatment groups, say Geerlings et al.

They conclude that despite the greater efficacy in preventing UTIs, use of TMP-SMX "should be weighed against the greater development of antibiotic resistance."

In an accompanying commentary, Bill Gurley (University of Arkansas for Medical Sciences, USA) highlighted that the comparative doses used in the study "may not have been fair in terms of dose and bioavailability of active ingredients."

He explained that the oral bioavailability of the active ingredient in cranberry extract was very low in comparison with that for TMP-SMX, at less than 10% versus 90%, suggesting that this was the reason "why the antibiotic was a more effective UTI preventative than cranberry extract."

MedWire ( is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2011

By Sarah Guy

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