Well, they really treat different things. I would want to know why your doctor is not using something like Bactrim/Septra. But the determination with urinary tract infections would be what kind of bacteria is causing the problem. I would assume that urine cultures and drug sensitivities have been done and without that, it really is guesswork as to which antibiotic will work best. Amazingly in my experience, neither of these drugs are common for UTIs.