How long does it take the antibiotic to work for a uti?

Hours to days: The antibiotic should begin to work - that is, kill bacteria - within hours. By a day or so, symptoms should be improving. Depending on how complicated the infection is and how long your course of antibiotics is for, it should be cleared within 3-14 days.

UTI: This varies with the type of uti, the antibiotic employed and its efficacy against the causative organism, the immune status and anatomical integrity of the urinary tract and other factors. Generally acute cystitis will begin to resolve symptomatically within 24-48 hrs after beginning appropriate treatment.

48 hrs: 48 hrs if taken oral.