BACKGROUND: Urinary tract infections (UTIs) are common among women and 
frequently recur. Depletion of vaginal lactobacilli is associated with UTI risk, 
which suggests that repletion may be beneficial. We conducted a double-blind 
placebo-controlled trial of a Lactobacillus crispatus intravaginal suppository 
probiotic (Lactin-V; Osel) for prevention of recurrent UTI in premenopausal 
women.
METHODS: One hundred young women with a history of recurrent UTI received 
antimicrobials for acute UTI and then were randomized to receive either Lactin-V 
or placebo daily for 5 d, then once weekly for 10 weeks. Participants were 
followed up at 1 week and 10 weeks after intervention and for UTIs; urine 
samples for culture and vaginal swabs for real-time quantitative 16S ribosomal 
RNA gene polymerase chain reaction for L. crispatus were collected.
RESULTS: Recurrent UTI occurred in 7/48 15% of women receiving Lactin-V compared 
with 13/48 27% of women receiving placebo (relative risk [RR], .5; 95% 
confidence interval, .2-1.2). High-level vaginal colonization with L. crispatus 
(≥10(6) 16S RNA gene copies per swab) throughout follow-up was associated with a 
significant reduction in recurrent UTI only for Lactin-V (RR for Lactin-V, .07; 
RR for placebo, 1.1; P < .01).
CONCLUSIONS: Lactin-V after treatment for cystitis is associated with a 
reduction in recurrent UTI. Larger efficacy trials of this novel preventive 
method for recurrent UTI are warranted. CLINICAL TRIALS REGISTRATION. 
NCT00305227.