The goal of this clinical trial is to learn if a common antibiotic called trimethoprim-sulfamethoxazole (TMP-SMX) can help prevent urinary tract infections (UTIs) in children and young adults who recently had a kidney transplant. Most people take TMP-SMX for about 6 months after getting a kidney transplant. In this study, researchers want to see what happens if people keep taking it for 6 more months.
The main questions this study is asking are:
* Does TMP-SMX lower the number of UTIs in the first year after transplant?
* What side effects or problems do participants have while taking TMP-SMX?
Researchers will compare TMP-SMX to a placebo (a look-alike pill that does not contain any medication) to see if TMP-SMX works to prevent UTIs.
Participants will:
* Take either TMP-SMX or a placebo pill by mouth every day for 6 months
* Have three visits to touch base with the study team about any issues
* Complete short monthly online surveys about any symptoms or side effects
* Share blood and urine test results from their regular transplant clinic visits