Most patients require therapy for 3 to 7 days. You should notice a reduction in your UTI symptoms during the first 1 to 2 days after taking your medicines. If your UTI is more severe or you've been experiencing symptoms for a time before taking antibiotics, it may take a few more days for you to notice an improvement. Continue taking Cephalexin for as long as your doctor advises, usually for the full course of treatment. Cephalexin works by stopping the growth of bacteria that cause urinary tract infections (UTIs). Bacteria cannot grow if there is no food or oxygen available. Ceftriaxone prevents the formation of new cells and new tissues by killing those already formed. Thus, it has a cytotoxic effect on rapidly dividing cells such as those found in cancerous tumors. It can also kill bacteria that are not susceptible to other antibiotics. This is important because even though you may have another infection at the same time as your UTI, treating the UTI with antibiotics will allow other infections to be cleared up too. Your doctor may suggest continuing Cephalexin beyond the typical duration of treatment for non-life-threatening UTIs. In these cases, it may be necessary to prevent further infections by clearing up any existing ones first. He or she may also prescribe this antibiotic in conjunction with other medications or treatments, such as surgery or self-care measures.