Hi, UTI is often diagnosed based on symptoms alone, and many women with a previous history of UTI can accurately know by themselves if they are having an episode of UTI. It is not uncommon to give Bactrim for UTI treatment without doing any testing. Penicillin is not the first choice of antibiotic for the treatment of UTI. It is only used in rare cases in the treatment of UTI, such as in pregnancy-associated with asymptomatic bacteriuria (Amoxicillin). I think that is the reason your doctor gave you Bactrim because he thought that Penicillin you took for your UTI did not cure it. Now regarding the side effects, Bactrim can cause liver damage, and certainly, if you have existing cirrhosis, it would be riskier. However, the duration of treatment for UTI is concise. So it depends on the clinical judgment of your doctor. If I were your doctor, I would have given you Ciprofloxacin, which is, as per clinical studies, safer to use in cirrhosis patients and more effective in treating Complicated UTI, which I suspect you have. Another thing to keep in mind is that untreated UTI can lead to more serious complications like Pyelonephritis, present with high-grade fever-like yours, and flank pain. If that s the case, you need to contact your doctor immediately or go to ER. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Saralkumar R. Desai, General & Family Physician