D-mannose

D-mannose is a naturally occurring, water soluble, simple sugar related to glucose.  It is found in small amounts in cranberry juice and cranberry concentrate.

D-mannose has an affinity for Escherichia coli bacteria, a.k.a. E. coli, an important and naturally occurring gastrointestinal microflora.  This E. coli bacteria is responsible for the vast majority of urinary tract infections (UTIs.)

When large doses of D-mannose are taken, the excess is secreted in the urine.
When D-mannose gets into the bladder and urinary tract, it can find E. coli bacteria and stick to the cell walls.  This can prevent the bacteria from attaching to the walls of the bladder and urinary tract, preventing the formation of bacterial colonies, and helping prevent future UTIs.  The coated bacteria are flushed away by the urine.  

D-mannose is different from an antibiotic.  It does not kill bacteria and it will not wash away bacteria already stuck to the bladder and urinary tract walls so it will not be effective in getting rid of a current UTI.  It does not coat E. coli bacteria in its natural location due to the location the D-mannose is absorbed inside the gastrointestinal tract.  

I have been unable to find evidence that D-mannose interferes with blood sugar regulation due to the very small amounts that are metabolized by the body.

Chance (60-ish lbs.) gets 2 grams per day.