A human study found that trimethoprim-sulfamethoxazole (TMP-SMX), an antibiotic, was more effective at preventing recurrent urinary tract infections (UTIs) among premenopausal females than cranberry capsules. The researchers, from the Academic Medical Center, Amsterdam, reported their findings in the journal Archives of Internal Medicine. They added that the antibiotic may raise the risk of resistance.

Recurrent UTIs are common among premenopausal females. Approximately half of all women are thought to be affected at some time. About 1 in every 3 women develops recurrent urinary tract infection. In such cases they are typically prescribed a low-dose antibiotic as a preventive measure.

The authors wrote:

“However, this may lead to drug resistance not only of the causative microorganisms but also of the indigenous flora.”

Although previous studies had demonstrated that cranberries and cranberry products can prevent UTIs, none of them ever compared the fruit with TMP-SMX, an antibiotic which is normally prescribed to prevent UTI recurrence.

Dr. MariГ«lle A.J. Beerepoot and team carried out a double-blind, non-inferiority trial comparing TMP-SMX with cranberry capsules. They recruited 221 patients, all of them premenopausal females who had had at least three UTIs during the previous twelve months.

The women were randomly selected into two groups:

TMP-SMX group – they took 480 mg of TMP-SMX every night, as well as one placebo capsule twice a day.
Cranberry group – they took 500mg of cranberry twice a day, as well as one placebo tablet at night.

They were checked once a month for UTI, and then for three months after the trial had ended. The women were given a questionnaire, and urine and feces samples were collected. Those who experienced UTI-like symptoms were asked to provide urine samples.

During the twelve-month period there were 1.8 recurrences in the TMP-SMX group compared to 4 in the cranberry group. The TMP-SMX group recurrences occurred after about 8 months, and 4 months in the cranberry group.

Antibiotic resistance tripled among those in the TMP-SMX group, but returned to normal 3 months after they discontinued with the medication.

TMP-SMX appears to be better at preventing UTI recurrences than cranberry tablets, the authors reported. However, there is the risk that this may be achieved with the price of higher antibiotic resistance.

The authors wrote:

“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. In those women, cranberry prophylaxis may be a useful alternative despite its lower effectiveness.”
Accompanying Commentary: Cranberries as Antibiotics?

Bill J. Gurley, Ph.D., from the University of Arkansas for Medical Sciences, Little Rock, commented on the team’s findings. He explained that although botanical dietary supplements are not specifically aimed at treating, curing or preventing illnesses..:

“..most U.S. consumers, however, have expectations of health benefits from the dietary supplements they consume.”

Such factors as poor water solubility, or the type of metabolism that occurs may interfere with cranberry capsule effectiveness, he wrote.

Cranberry’s much lower risk of antibiotic resistance certainly makes it a useful preventive substance for recurring, UTIs, he wrote.

“..such a marked reduction in antibiotic resistance certainly favors the therapeutic potential of cranberry as a natural UTI preventative.”

Gurley added:

“Because optimal doses have not been established for many botanicals, clinical efficacy trials have often yielded negative or inconclusive results.”

Further studies, using varying doses of cranberry products may provide more useful data on effectiveness.

Arch Intern Med. 2011;171[14]:1270-1278