The antiseptic methenamine hippurate (MH) is known to sterilize urine and has been suggested to be of use in preventing urinary tract infections (UTIs), but firm evidence has so far been lacking. Now researchers led by clinicians and scientists from Newcastle-upon-Tyne, England, have provided the ALTAR trial (Alternative to Prophylactic Antibiotics for the Treatment of Recurrent UTIs in Women).
Daily low-dose antibiotics as recommended by current guidelines for prophylactic treatment of recurrent UTI have been linked to antibiotic resistance. Using MH as an alternative could play an important role in helping to tackle the global problem of increasing antibiotic resistance, the team said.
They recruited 240 women aged 18 or over with recurrent UTIs requiring prophylactic treatment from eight secondary care urology and urogynecology centers in the United Kingdom from June 2016 to June 2018. Women were randomized to receive MH or daily low-dose antibiotics for 12 months, with follow up for a further 6 months beyond that.
Before trial entry the women had experienced an average of more than six UTI episodes per year. During the 12-month treatment period, in the modified intention-to-treat population, there were 90 symptomatic, antibiotic-treated UTI episodes reported over 101 person-years of follow-up in the antibiotic group, and 141 episodes over 102 person-years in the MH group.
This yielded a UTI rate of 0.89 episodes per person-year in the antibiotic group, compared with 1.38 in the MH group, an absolute difference of 0.49 episodes per person-year. In the 6-month posttreatment follow-up period, the UTI incidence rate was 1.19 episodes per person-year in the antibiotic prophylaxis group versus 1.72 in the MH group, an absolute difference of 0.53.
Before the trial, a patient and public involvement group had predefined the noninferiority margin as one episode of UTI per person-year. The small difference between the two groups was less than this, confirming noninferiority of MH to antibiotic prophylaxis in this setting. This finding was consistent across the modified intention-to-treat, strict intention-to-treat, per protocol, and modified per protocol (post hoc) analyses.
Thus the ALTAR results showed that MH was no worse than antibiotics at preventing UTIs, and MH was also associated with reduced antibiotic consumption.
The vast majority of participants were over 90% adherent with the allocated treatment. Patient satisfaction was generally high and rates of adverse events and adverse reactions generally low, and both were comparable between treatment groups. Adverse reactions were reported by 34/142 (24%) in the antibiotic group and 35/127 (28%) in the MH group, and most reactions were mild. In the antibiotic group there were two serious adverse reactions (severe abdominal pain and raised alanine transaminase), whereas six participants in the MH group reported an episode of febrile UTI and four were admitted to hospital because of UTI.
Substantial global health care problem
At least 50% and up to 80% of all women have at least one acute UTI in their lifetime, most often uncomplicated acute cystitis. About a quarter of them go on to suffer recurrent infection, defined as three or more repeat infections in the past year, or two infections in the preceding 6 months. Frequent recurrences thus represent “a substantial global health care problem,” the authors say.
Guidelines from the United Kingdom, Europe, and the United States acknowledge the need for preventive strategies and strongly recommend the use of daily, low-dose antibiotics as standard prophylactic treatment. However, the United Kingdom’s antimicrobial resistance strategy recommends a “strong focus on infection prevention,” and aims to reduce antimicrobial use in humans by 15% before 2024.
“To achieve that, exploration of nonantibiotic preventive treatments in common conditions such as UTI is essential,” the team said.
MH is one such nonantibiotic treatment. It is bactericidal and works by denaturing bacterial proteins and nucleic acids. Although previous Cochrane systematic reviews had concluded that it could be effective for preventing UTI, further large trials were needed.
“This trial adds to the evidence base for the use of MH for prophylactic treatment in adult women with recurrent UTI. Although the MH group had a 55% higher rate of UTI episodes than the antibiotics group, the absolute difference was just 0.49 UTI episodes per year, which has limited clinical consequence,” the team concluded.
Results could ‘support a change in practice’
In older patients, particularly, the risks of long-term antibiotic prophylaxis might outweigh the benefits, and the authors said that their results “could support a change in practice in terms of preventive treatments for recurrent UTI and provide patients and clinicians with a credible alternative to daily antibiotics, giving them the confidence to pursue strategies that avoid long-term antibiotic use.”
They acknowledged limitations of the study, including that treatment allocation was not masked, crossover between arms was allowed, and differences in antibiotics prescribed may have affected the results. In addition, data regarding long-term safety of MH are scarce.
However, they said that the trial accurately represented the broad range of women with recurrent UTI, and that its results “might encourage patients and clinicians to consider MH as a first line treatment for UTI prevention in women.”
In a linked editorial, scientists from the Institute for Evidence-Based Healthcare at Bond University in Queensland, Australia, commented: “Although the results need cautious interpretation, they align with others, and this new research increases the confidence with which MH can be offered as an option to women needing prophylaxis against recurrent urinary tract infection.”
Alternative to prophylactic antibiotics for the treatment of recurrent urinary tract infections in women: multicentre, open label, randomised, noninferiority trial. BMJ 2022 Mar 9;376:e068229.
Methenamine hippurate for recurrent urinary tract infections. BMJ 2022 Mar 9;376:o533.
A version of this article first appeared on.