For nearly a year, our dog was notorious for getting bladder infections as soon as the antibiotics wore off. Every antibiotic was tried including sulfur medications. It didn't help that every time we took her in....different vet saw her and everyone had their own medication that they wanted to try. Finally the vet we preferred saw her again, isolated a clean specimen (by inserting a needle directly into her bladder) and somehow was able to culture it and determine through process of elimination (on the culture) which antibiotic was the best suited to get rid of the infection. Naturally it was the most expensive antibiotic which cost about $250 or more. Then our dog was put on Science Diet C/D food to make her urine more acidic. After that...no more infections. She continued this food for 9 years until she was too old (16 years old) and was put to rest last November.