Patients with recurrent UTI were randomized to receive either the probiotic Sacchromyces Boulardii at enrollment, and the intracellularly active Ciprofloxacin with their first UTI episode after enrollment, or they received standard of care treatment.

• At the time of consent, participants will be given 20 mg/kg of the antibiotic, ciprofloxacin. If the participant has symptoms of a UTI or have a positive urine culture at enrollment, they will take the antibiotic every 12 hours for 14 days. If the participant does not have symptoms of a UTI at enrollment, the antibiotic will be taken only if needed at home upon the first occurrence of a UTI.
• At the time of consent, participants will also be given 250 mg of the probiotic, S.

boulardii, taken once daily for 6 months, irrespective of symptoms.

- Throughout the study, participants will receive their standard clinical care for recurrent UTI treatment, which includes bowel and bladder dysfunction management and other prescribed non-antibiotic interventions at the managing provider's clinical discretion.

Inclusion Criteria:

• A history of 3 or more UTI episodes in the past 12 months, or 2 or more episodes in the past 6 months
• no evidence of vesicoureteral reflux or only low-grade (grade 1-2) vesicoureteral reflux
• no other genitourinary anatomical abnormality
• not receiving prophylactic antibiotics at the time of enrollment
• Ages 2-17 years.

Exclusion Criteria:

• high grade (grade 3-5) vesicoureteral reflux
• neurogenic bladder
• anatomical abnormalities of the gastrointestinal tract
• any history of urologic or gastrointestinal surgery
• on prophylactic antibiotics
• a urine culture positive for pathogens that are not susceptible to ciprofloxacin in the last 3 months
• history of an allergic reaction to ciprofloxacin or other quinolones, or a history of severe adverse reactions
• As stated on the package insert for Ciprofloxacin, individuals with a known history of myasthenia gravis should avoid taking Ciprofloxacin and therefore will be excluded from this study.
• Based on the black box warning for Ciprofloxacin, individuals taking tizanidine as concomitant administration, or those taking other drugs known to interact with ciprofloxacin will be excluded from the study.
• individuals with known QT prolongation, hypokalemia, or on other drugs that prolong the QT interval should also avoid taking Ciprofloxacin and will be excluded from this study.
• Individuals under 2 years old. In the BFIT clinic, because they do bladder, bowel movement, and constipation management, it is harder to manage if the patient is not potty trained. Therefore, we are excluding participants under 2 years of age.