Microbiome-Modulating Prophylaxis RCT: Antibiotic vs Gynoflor in Postmenopausal Women With Recurrent Cystitis

Inclusion Criteria: * Female, postmenopausal, age ≥40 years * Clinical history of recurrent urinary tract infection (rUTI) as assessed by the investigator * Able and willing to take assigned prophylaxis for 6 months * Able to attend baseline and Month 6 study visits and provide urine samples * Able to provide written informed consent * Willing and able to complete twice-weekly phone/LINE follow-ups Exclusion Criteria: * Current symptomatic UTI at enrollment (may be treated and reconsidered after resolution) * Known hypersensitivity or contraindication to nitrofurantoin or to the Lactobacillus/estriol vaginal tablet (Gynoflor) or their excipients; significant renal impairment or other label-based contraindications to nitrofurantoin per local practice * Planned urologic surgery or procedure expected during the 6-month study period * Recent bacterial vaginosis (e.g., within the past month) or active vulvovaginal skin disorders precluding vaginal product use * History of hormone-dependent malignancy (e.g., breast, uterine, or cervical cancer) or unexplained abnormal vaginal bleeding * Significant liver disease (e.g., active hepatitis) or other conditions judged by the investigator to make participation unsafe * Participation in another interventional trial that could interfere with outcomes * Withdrawal of consent or severe adverse event requiring discontinuation