A single centre proof of concept study to assess whether Vitamin C improves the efficacy of Methenamine Hippurate (Hiprex®) in the prophylaxis of recurrent urinary tract infections (rUTIs) in women

Inclusion Criteria:

• Female
• Age ≥18 years
• Recurrent proven UTI, defined as "two or more proven infections in six months or three or more infections in six months"
• Willing and able to give fully informed consent
• Patients suitable for prophylaxis following discussion with their clinician.
• No contra-indications to treatment with methenamine hippurate or Vitamin C
• All women will have undergone standard diagnostic work-up and have followed routine conservative UTI prevention measures.
• A working email address to be used to submit urine pH results
• Willing and able to comply with the study procedures
• Females of childbearing potential must be willing to use a highly effective method of contraception (hormonal or barrier method of birth control; abstinence; sterilisation or vasectomised partner)

Exclusion Criteria:

• Males
• Women who are pregnant or breast-feeding
• Contraindications to methenamine hippurate as described in BNF: known allergy, gout, severe metabolic acidosis, severe dehydration, eGFR less than 10 ml/min, severe hepatic impairment
• Currently using vitamin C containing supplement or cranberry extract tablets
• Women using urinary alkalinisation agents, e.g potassium citrate, sodium bicarbonate
• Currently receiving any form of bladder instillation or intradetrusor Onabotulinum Toxin A injections
• Patients already on low-dose antibiotics or methenamine hippurate (due to delay that will be incurred by 3-month washout period)
• Indwelling urinary catheter in situ or performing clean intermittent self-catheterisation
• Correctable urinary tract abnormalities, e.g., urinary tract calculi, urinary retention
• Formation of ileal conduit or augmented bladder
• Neurogenic bladder dysfunction
• Hyperoxaluria