@calicat Hello, I had to look this up, as my husband with diabetes also sometimes gets UTI's
According to WebMD, "d mannitol" is the sugar-acid form of the simple sugar "d mannose", which is found in a number of fruits, legumes and other foods.
There are medical applications for d mannitol, including the possible effect of preventing or treating UTI's, but the current recommendation is to use only under doctor's supervision.
There are also reports that d mannose helps with UTI's, but does carry the risk of increasing blood sugar in people with diabetes. (https://www.webmd.com/vitamins-and-supplements/d-mannose-uses-and-risks)

So, the recommendation is to work with your doctor in trying it. Do you think your doctor would be open to such a trial?
Sue