In premenopausal（绝经前期的） women who have repeated urinary tract（泌尿道） infections (UTIs), the antibiotic trimethoprim-sulfamethoxazole (TMP-SMX) appeared more effective than cranberry（蔓越橘） capsules for preventing recurrent infections, at the risk of contributing to antibiotic resistance, according to a report in the July 25 issue of Archives of Internal Medicine, one of the JAMA/Archives journals. Urinary tract infections are common in women, affecting nearly half at some point in their lives, according to background information in the article. The authors note that up to 30 percent of women develop recurrent UTIs (rUTIs), a condition for which a low-dose antibiotic is frequently used as a preventive measure. "However, this may lead to drug resistance not only of the causative microorganisms but also of the indigenous flora（土著菌群） ," write the authors. Studies of cranberries and cranberry products have shown some effectiveness in preventing rUTIs, but these trials have not compared those interventions directly with TMP-SMX, the standard antibiotic used in these cases.

Mariëlle A.J. Beerepoot, M.D., from the Academic Medical Center, Amsterdam, and colleagues conducted a double-blind noninferiority trial of cranberry capsules and TMP-SMX. The 221 participants were premenopausal adult women who had reported at least three symptomatic UTIs in the previous year. They were randomized to take either TMP-SMX (480 mg at night, plus one placebo capsule twice daily) or cranberry capsules (500 mg twice daily, plus one placebo tablet at night) for 12 months. Researchers assessed participants' clinical status once a month (and for three months after stopping the study medication) via urine and feces samples and a questionnaire; participants also submitted urine samples when they experienced UTI-like symptoms.

At 12 months, the average number of clinical recurrences was 1.8 in the TMP-SMX group and 4.0 in the cranberry capsules group. Recurrence occurred, on average, after eight months in the drug group and after four months in the cranberry capsules group. Antibiotic resistance rates tripled in the pathogens found in patients in the TMP-SMX group, although three months after the drug was discontinued, resistance rates returned to the levels they had been at when the study began.

The antibiotic used in this study appeared to be more effective at preventing rUTIs than cranberry capsules, but the researchers noted that achieving this result also seemed to increase the rate of antibiotic resistance. "From clinical practice and during the recruitment phase of this study, we learned that many women are afraid of contracting drug-resistant bacteria using long-term antibiotic prophylaxis and preferred either no or nonantibiotic prophylaxis（预防） ," they report. "In those women, cranberry prophylaxis may be a useful alternative despite its lower effectiveness."