My cat had the same thing for awhile...
She was VERY over weight that's what was causing it.
My vet didn't give me anything for her but some special cat food for it.
We tried this and it didn't work we just cut her back too half a cup of food and day and she's all better..
Maybe is your cat is fat you should just put him on a diet.
I haven't seen bloody pee from her for quite sometime now.
Accio isn't overweight, he's a big cat but he's just a big cat and the right weight for his height. He was diagnosed with Chronic Cystitis which cannot be controlled by certain foods.