Cranberry and urinary tract infections: slightly fewer episodes in young women, but watch out for interactions.

(1) Female urinary tract infections are common and often recurrent. Food supplements based on cranberries are said to prevent recurrent urinary tract infections. (2) Two randomised controlled trials involving a total of about 300 young women showed that daily use of cranberry juice or tablets reduced the relapse rate for acute cystitis: on average, treating 100 women for one year prevented at least 1 urinary tract infection in 15 to 33 women. The daily doses were 7.5 g of concentrate in 50 ml of water, 750 ml of juice, or two tablets of concentrate. (3) In elderly patients, 2 trials of cranberry-based products in hospitals or nursing homes showed a small reduction in the frequency of relapses. (4) Adverse effects appear to be negligible. However, several case reports of interactions with warfarin have been published, including one involving severe bleeding. Patients on vitamin K antagonists must be warned about this risk of interactions so that they avoid consuming cranberry-based products without medical supervision.