Similar to a PP, I was prescribed nitrofurantoin as a preventative after years of recurring UTIs.
I'm sure I was fine for the first few days, maybe longer, but after a particularly long walk in the cold I came over intensely fatigued - collapsed into bed thinking I was coming down with flu, my chest was burning. Within 12 hrs I was coughing up weird white froth and I was short of breath.
Went to GP who sent me straight to hospital with a suspected pulmonary embolism. Long story short, after scratching their heads for 3 days about why my d-dimer was off the charts, a scan revealed no clots. I continued on the nitrofurantoin, breathless and with pain in my upper back, for 3 months.
It resolved my UTIs for about 3 years until I got another one, and I started the nitrofurantoin again. This time, the acute pulmonary response kicked in vigorously after 24 hrs, the GP surgery recognised it as a reaction and now it's listed as a serious allergy.
Trimethoprim is ok for me although it makes me feel a bit sick, I'm allergic to penicillin but for the last UTI I was prescribed Cefalexin (which I was too nervous to take, given it's link to penicillin).
I have a chronically painful urethra, poor urinary flow, urinary hesitancy, high levels of uric acid in my blood tests, and my pee smells like Satan's armpit. But there doesn't seem to be any long term curative treatment suggested.