In short
Methenamine hippurate is a chemical antiseptic medicine used to prevent recurrent urinary tract infections (UTIs). It is not an antibiotic and cannot treat an existing UTI. One Phase 3 trial with 204 women is comparing methenamine hippurate against antibiotic prophylaxis for recurrent UTIs, measuring both UTI episodes and the development of multidrug-resistant bacteria.
Key points
- Methenamine hippurate is an antiseptic, not an antibiotic, used to prevent urinary tract infections.
- It works by releasing formaldehyde in the urine, which stops bacteria from growing.
- A Phase 3 trial is testing methenamine hippurate against antibiotics in 204 women with recurrent UTIs.
- The trial measures the number of UTI episodes and the emergence of multidrug-resistant bacteria over 6 months.
- Methenamine hippurate is authorised as a medicine and is available under brand names such as Hiprex and Urex.
- A 2022 trial found methenamine hippurate was as good as antibiotics for preventing recurrent UTIs in women.
What is methenamine hippurate?
Methenamine hippurate is a chemically synthesised antiseptic medicine used to prevent urinary tract infections (UTIs) caused by bacteria. It belongs to the therapeutic area of female urogenital diseases and is taken by mouth. It is not an antibiotic and will not treat a UTI that is already present. Methenamine hippurate is authorised as a medicine and is known under the brand names Hiprex and Urex.
How does methenamine hippurate work?
Methenamine hippurate acts as a bacteriostatic agent, meaning it stops bacteria from multiplying rather than killing them directly. In the urine, the substance is converted into formaldehyde from hexamine, and this formaldehyde prevents the growth of certain bacteria. This mechanism is not known to cause antibiotic resistance, which makes it a candidate for long-term prevention of recurrent UTIs. A Newcastle-led study described the drug as sterilising urine and stopping the growth of certain bacteria.
Which conditions is methenamine hippurate used or studied for?
- Recurrent urinary tract infections (rUTIs) in women — the main condition studied in the registered Phase 3 trial.
- Urinary tract infections (UTIs) caused by bacteria — the condition for which methenamine hippurate is used as a preventive medicine.
- Recurrent UTIs in older women — an area of ongoing research, with a randomised, placebo-controlled trial protocol published in 2022.
How is methenamine hippurate given?
Methenamine hippurate is given orally, in tablet form. The registered trial uses a dose of 2 grams taken by mouth. The product information instructs that the tablets should be taken with a full glass of water and should not be crushed or chewed.
What do the clinical trials show?
One Phase 3 clinical trial is registered for methenamine hippurate in recurrent urinary tract infections. The trial plans to enrol 204 women and is currently authorised. The study compares methenamine hippurate against three antibiotic comparators: co-trimoxazole (Septrin), cefalexin and fosfomycin trometamol.
In addition to this registered trial, a 2022 randomised trial led by Newcastle Hospitals compared daily methenamine hippurate with daily antibiotics in women with recurrent UTIs. In that study, 103 women received methenamine hippurate and 102 received antibiotics for 12 months. The findings, published in the British Medical Journal, showed that methenamine hippurate was as good as antibiotics for preventing recurrent UTIs.
The primary outcomes of the registered Phase 3 trial are the number of recurrent symptomatic UTI episodes during a 6-month treatment period and the number of patients with isolates showing a multidrug-resistant (MDR) profile at 6 months. A systematic review and meta-analysis of six studies with 557 women found insufficient evidence to be certain of the benefits of methenamine hippurate for preventing UTIs in community adult women.
What side effects are known?
The supplementary sources provided do not include a detailed side effect profile for methenamine hippurate. The Cleveland Clinic source notes that people should tell their care team if they have kidney disease, liver disease, dehydration, or an unusual or allergic reaction to methenamine or tartrazine dye before taking this medication.