Hello, I m 76 yrs old and keep getting UTI s and they give me Keflex because I m allergic to some of the other drugs used to treat this. The problem is, after I m finished with Keflex the UTI comes back again. So we re thinking that its not strong enough to kill the bacteria or I ve become immune to it. I ve taken Zirthomax in the past to treat something else, so I don t think I m allergic to it.. Would you recommend trying that drug next? (cannot take Sulfa meds, don t want to take Cipro)