Why Dose Matters

pills_2348412bLast week, media outlets were quick to pick up the story of a research study[1] that showed cranberry extract isn’t as effective as antibiotics for the prevention of recurrent urinary tract infections (UTIs). The headlines were consistent: “Antibiotics beat cranberries,”[2] “Don’t bet on cranberry,”[3] and “Cranberries little help”[4].  Unfortunately, what is lacking from many of the medical news reports is a critical review of the study’s methodology and thus the validity and applicability of its results.  While a study comparing the efficacy of antibiotics and cranberry is a great idea, the cranberry extract studied contained the daily equivalent of merely 9.1 mg of proanthocyanidins, the key chemical constituent responsible for protecting against adherence of bacteria in the urinary tract.   This dose falls far short of the 72 mg daily dose of proanthocyanidins currently accepted as the most effective based on recent clinical studies[5], a problem admitted by the study’s authors in discussing their results.

Even at such a low dose, cranberry showed great promise.

After 12 months of taking either trimethoprim-sulfamethoxazole (TMP-SMX, 480 mg once daily) or cranberry capsules (500 mg, containing 4.55 mg of proanthocyanidins, twice daily):

  • the mean number of women experiencing at least 1 UTI was greater in the cranberry than the antibiotic group (4.0 vs 1.8; p=0.02)
  • the proportion with at least 1 UTI was also greater in the cranberry group (78.2% vs 71.1%; p=0.03)
  • median time to first UTI was 4 months in the cranberry group, vs. 8 months in the antibiotic group
  • 86.3% of fecal and 90.5% of asymptomatic bacteriuria E coli isolates were TMP-SMX resistant vs. 23.7% and 28.1% in the cranberry group
  • increased resistance rates for was other types of antibiotics were also found in the TMP-SMX group after 1 month
  • antibiotic resistance did not increase in the cranberry group

As noted by Galen’s Watch, “As part of a total treatment that included other supplements that have shown benefit in preventing UTI’s such as probiotics and vitamin C the outcome could be quite different. A typical treatment plan could include dietary recommendations and herbs, among other things.”[6]  All is not lost for cranberry.  At the correct dose, it remains an important part of a holistic approach to preventing UTIs.

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  1. Beerepoot MAJ et al. Cranberries vs antibiotics to prevent urinary tract infections. A randomized double-blind noninferiority trial in premenopausal women. Arch Intern Med [serial on the internet]. 2011 [cited 2011 July 30];171(14):1270-1278. Available from: http://archinte.ama-assn.org/cgi/content/short/171/14/1270.
  2. Freeman DW. For urinary tract infection, antibiotics beat cranberries. CBS News [website]. 2011 July 26 [cited 2011 July 30]. Avail­able from: http://www.cbsnews.com/8301-504763_162-20083454-10391704.html.
  3. Gardner A. Don’t bet on cranberry against UTIs. CNN [website]. 2011 July 25 [cited 2011 July 30]. Avail­able from: http://www.cnn.com/2011/HEALTH/07/25/antibiotics.cranberry.upi.prevention/.
  4. Walsh N. Cranberries little help for bladder. MedPageToday [website]. 2011 July 25 [cited 2011 July 30]. Available from: http://www.medpagetoday.com/InfectiousDisease/GeneralInfectiousDisease/27725.
  5. Howell AB et al. Dosage effect on uropathogenic Escherichia coli anti-adhesion activity in urine following consumption of cranberry powder standardized for proanthocyanidin content: a multicentric randomized double blind study. BMC Infect Dis [serial on the internet]. 2010 [cited 2011 July 30];10:94. Available from: http://www.biomedcentral.com/1471-2334/10/94#B12.
  6. Way S. Antibiotics beat Cranberries for UTI’s? Not so fast… Galen’s Watch

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    . 2011 July 26 [cited 2011 July 30]. Available from: http://camwatcher.typepad.com/cam_watcher/2011/07/antibiotics-beat-cranberries-for-utis-that-is-what-the-headlines-say-but.html.
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