Methenamine hippurate compared with antibiotic prophylaxis to prevent recurrent urinary tract infections in women: the ALTAR non-inferiority RCT
Authors: Harding Chris , Chadwick Thomas , Homer Tara , Lecouturier Jan , Mossop Helen , Carnell Sonya , King Will , Abouhajar Alaa , Vale Luke , Watson Gillian , Forbes Rebecca , Currer Stephanie , Pickard Robert , Eardley Ian , Pearce Ian , Thiruchelvam Nikesh , Guerrero Karen , Walton Katherine , Hussain Zahid , Lazarowicz Henry , Ali Ased 
Published: May 2022

BackgroundDaily, low-dose antibiotic prophylaxis is the current standard care for women with recurrent urinary tract infection. Emerging antimicrobial resistance is a global health concern, prompting research interest in non-antibiotic agents such as methenamine hippurate, but comparative data on their efficacy and safety are lacking.ObjectiveTo assess the clinical effectiveness and cost-effectiveness of methenamine hippurate (Hiprex®; Mylan NV, Canonsburg, PA, USA) compared with current standard care (antibiotic prophylaxis) for recurrent urinary tract infection prevention in adult women.DesignMulticentre, pragmatic, open-label, randomised, non-inferiority trial of 12 months’ treatment with the allocated intervention, including an early, embedded qualitative study and a 6-month post-treatment observation phase. The predefined non-inferiority margin was one urinary tract infection per person-year.SettingEight UK NHS secondary care sites.ParticipantsA total of 240 adult women with recurrent urinary tract infection requiring preventative treatment participated in the trial.InterventionsA central randomisation system allocated participants 1 : 1 to the experimental (methenamine hippurate: 1 g twice daily) or control (once-daily low-dose antibiotics: 50/100 mg of nitrofurantoin, 100 mg of trimethoprim or 250 mg of cefalexin) arm. Crossover between treatment arms was permitted.Main outcome measuresThe primary clinical outcome was incidence of symptomatic antibiotic-treated urinary tract infection during the 12-month treatment period. Cost-effectiveness was assessed by incremental cost per quality-adjusted life-year gained, extrapolated over the patient’s expected lifetime using a Markov cohort model. Secondary outcomes included post-treatment urinary tract infections, total antibiotic use, microbiologically proven urinary tract infections, antimicrobial resistance, bacteriuria, hospitalisations and treatment satisfaction.ResultsPrimary modified intention-to-treat analysis comprised 205 (85%) randomised participants [102/120 (85%) participants in the antibiotics arm and 103/120 (86%) participants in the methenamine hippurate arm] with at least 6 months’ data available. During treatment, the incidence rate of symptomatic, antibiotic-treated urinary tract infections decreased substantially in both arms to 1.38 episodes per person-year (95% confidence interval 1.05 to 1.72 episodes per person-year) for methenamine hippurate and 0.89 episodes per person year (95% confidence interval 0.65 to 1.12 episodes per person-year) for antibiotics (absolute difference 0.49; 90% confidence interval 0.15 to 0.84). This absolute difference did not exceed the predefined, strict, non-inferiority limit of one urinary tract infection per person-year. On average, methenamine hippurate was less costly and more effective than antibiotics in terms of quality-adjusted life-years gained; however, this finding was not consistent over the longer term. The urinary tract infection incidence rate 6 months after treatment completion was 1.72 episodes per year in the methenamine hippurate arm and 1.19 in the antibiotics arm. During treatment, 52% of urine samples taken during symptomatic urinary tract infections were microbiologically confirmed and higher proportions of participants taking daily antibiotics (46/64; 72%) demonstrated antibiotic resistance inEscherichia colicultured from perineal swabs than participants in the methenamine hippurate arm (39/70; 56%) (p-value = 0.05). Urine cultures revealed that during treatment higher proportions of participants and samples from the antibiotic arm grewE. coliresistant to trimethoprim/co-trimoxazole and cephalosporins, respectively. Conversely, post treatment, higher proportions of participants in the methenamine hippurate arm (9/45; 20%) demonstrated multidrug resistance inE. coliisolated from perineal swabs than participants in the antibiotic arm (2/39; 5%) (p = 0.06). All other secondary outcomes and adverse events were similar in both arms.LimitationsThis trial could not define whether or not one particular antibiotic was more beneficial, and progressive data loss hampered economic evaluation.ConclusionsThis large, randomised, pragmatic trial in a routine NHS setting has clearly shown that methenamine hippurate is not inferior to current standard care (daily low-dose antibiotics) in preventing recurrent urinary tract infections in women. The results suggest that antimicrobial resistance is proportionally higher in women taking prophylactic antibiotics.Recommendations for researchFuture research should include evaluation of other non-antibiotic preventative treatments in well-defined homogeneous patient groups, preferably with the comparator of daily antibiotics.Trial registrationThis trial is registered as ISRCTN70219762 and EudraCT 2015-003487-36.FundingThis project was funded by the National Institute for Health and Care Research (NIHR) Health Technology Assessment programme and will be published in full inHealth Technology Assessment; Vol. 26, No. 23. See the NIHR Journals Library website for further project information.