the are bacteria, hence a antibiotic. They can become immune to certain medicines if this is a consistent problem and same medicine and dose is prescribed, but if you are doing pres. 100% correctly, times and everything it should be fully treated, when you stop giving medicine because you think its better without treating for the several days is when most people have trouble. Your vet. should be able to try a different prescription if your cat is consistently getting UTI's, but if its a male I could be more concerned with kidney function and stones, get a water that flows and filters, cats can be finicky and if they are not drinking enough it only makes matters worse.
veterinary asst., dog trainer, cat owner