SN instructed patient that Bactrim DS is an antibiotic used to treat Urinary tract Infection ( UTI ). Instructed to use this medication for the full prescribed length of time. Your symptoms may improve before the infection is completely cleared. Skipping doses may also increase your risk of further infection that is resistant to antibiotics. Instructed the most common side effects have included nausea, vomiting, anorexia, rash, and urticaria. Instructed to notify physician ( MD ) of any side effects.