The best way to treat UTIs in the elderly, or anyone for that matter, is to try to prevent their occurrence. UTIs can be prevented or their recurrence minimized by:
Not using douches or other feminine hygiene products
Not drinking fluids that tend to irritate the bladder, such as alcohol and caffeine
Drinking cranberry juice or taking cranberry supplement tablets, but only if you or your family does not have a history of kidney stones
Drinking lots of water
Keeping the genital area clean. If wearing adult diapers see that they are changed regularly. Wear cloth undergarments
Always wiping from front to back (for women)