Best Answer: No. It is unlikely to be effective. By far the most common bacteria that causes UTI (urinary tract infection) is E. coli. Sulfa (Bactrim, Septra), nitrofurantoin (Macrodantin), Ampicillin, and ciprofloaxacin (Cipro) are prescribed to treat bladder infection (UTI). Doxycycline is ineffective against E. coli and most UTIs. The best way to be sure (but most expensive) is to go to the doctor and get a urinalysis to confirm that it's a bladder infection and to have a urine Culture and Sensitivity sent off.