Effect of urinary acidifiers on formaldehyde concentration and efficacy with methenamine therapy

Methenamine for urinary tract infection prophylaxis: A systematic review

Urinary tract infections (UTIs) commonly affect many patient populations. Recurrent UTIs (rUTIs) can be particularly problematic and lead to potential hospitalizations, multiple antibiotic courses, and have a potential negative impact on quality of life. To prevent UTIs, antibiotics are frequently used for prophylaxis; however, antibiotic prophylaxis has notable untoward consequences including but not limited to potential adverse effects and development of antibiotic resistance. Methenamine, an antiseptic agent initially available in 1967, has re-emerged as a potential option for UTI prophylaxis in various populations, including older adults and renal transplant recipients. The objective of this systematic review was to evaluate the clinical effectiveness and safety of methenamine for UTI prophylaxis. A systematic review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidance was performed. A PubMed, Embase, and Cochrane library search was conducted to identify relevant English-language studies evaluating methenamine for UTI prophylaxis including randomized controlled trials, case-control studies, and meta-analyses through June 2023. Articles were excluded if the studies did not primarily describe or evaluate methenamine for UTI prophylaxis, were commentaries/viewpoints articles, point prevalence studies, review articles, studies that evaluated methenamine used with another agent, and any duplicate publications from searched databases. A total of 11 articles were identified for inclusion. This systematic review suggests methenamine generally appears to be an effective and well-tolerated antibiotic-sparing option for UTI prophylaxis. Furthermore, the pharmacology, dosage and formulation, warnings, precautions, and safety considerations of methenamine that provide potential clinical considerations regarding its use for UTI prophylaxis are described. Further studies are needed to evaluate the clinical utility of methenamine for UTI prophylaxis.

Cranberries for treating urinary tract infections

BACKGROUND

Cranberries (particularly in the form of cranberry juice) have been used widely for several decades for the prevention and treatment of urinary tract infections (UTIs). The aim of this review is to assess the effectiveness of cranberries in treating such infections.

OBJECTIVES

To assess the effectiveness of cranberries for the treatment of UTIs.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Register of Studies up to 1 August 2023 through contact with the Information Specialist using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Registry Portal (ICTRP) Search Portal and ClinicalTrials.gov.

SELECTION CRITERIA

All randomised controlled trials (RCTs) or quasi-RCTs of cranberry juice or cranberry products for the treatment of UTIs. Studies of men, women or children were to be included.

DATA COLLECTION AND ANALYSIS

Titles and abstracts of studies that were potentially relevant to the review were screened and studies that were clearly ineligible were discarded. Further information was sought from the authors where papers contained insufficient information to make a decision about eligibility.

MAIN RESULTS

No studies were found that fulfilled all of our inclusion criteria. Seven studies were excluded because they were the wrong study design, mixed interventions or did not report any relevant outcomes. One study is ongoing; however, its current status is unknown.

AUTHORS' CONCLUSIONS

After a thorough search, no RCTs which assessed the effectiveness of cranberry juice for the treatment of UTIs were found. Therefore, at the present time, there is no good quality evidence to suggest that it is effective for the treatment of UTIs. Well-designed parallel-group, double-blind studies comparing cranberry juice and other cranberry products versus placebo to assess the effectiveness of cranberry juice in treating UTIs are needed. Outcomes should include a reduction in symptoms, sterilisation of the urine, side effects and adherence to therapy. The dosage (amount and concentration) and duration of therapy should also be assessed. Consumers and clinicians will welcome the evidence from these studies.

Nonantibiotic prevention and management of recurrent urinary tract infection

Urinary tract infections (UTIs) are highly prevalent, lead to considerable patient morbidity, incur large financial costs to health-care systems and are one of the most common reasons for antibiotic use worldwide. The growing problem of antimicrobial resistance means that the search for nonantibiotic alternatives for the treatment and prevention of UTI is of critical importance. Potential nonantibiotic measures and treatments for UTIs include behavioural changes, dietary supplementation (such as Chinese herbal medicines and cranberry products), NSAIDs, probiotics, D-mannose, methenamine hippurate, estrogens, intravesical glycosaminoglycans, immunostimulants, vaccines and inoculation with less-pathogenic bacteria. Some of the results of trials of these approaches are promising; however, high-level evidence is required before firm recommendations for their use can be made. A combination of these agents might provide the optimal treatment to reduce recurrent UTI, and trials in specific population groups are required.

Methenamine: a forgotten drug for preventing recurrent urinary tract infection in a multidrug resistance era

In the era of multidrug resistance, it is critical to utilize antibiotics in an appropriate manner and to identify new treatments or revisit the use of 'forgotten' drugs. Because urinary tract infections (UTIs) are common, particularly in an increasing elderly population, the 'forgotten' drug, methenamine, may become important as a preventive therapy for recurrent UTIs. Methenamine, a urinary antibacterial agent, can be used as methenamine hippurate or methenamine mandelate preparations and is United States Food and Drug Administration-approved. This article discusses the place of preventive therapy for recurrent UTIs, chemistry, mechanism of action, pharmacology, clinical uses, dosage, adverse reactions and safety, and drug interactions of methenamine. Because of its unique antiseptic property, the authors suggest that methenamine should be considered when more commonly used antibiotics fail to suppress recurrent UTIs.

Methenamine hippurate for preventing urinary tract infections

BACKGROUND

Methenamine salts are often used as an alternative to antibiotics for the prevention of urinary tract infection (UTI). This review was first published in Issue 1, 2002 and updated in Issue 4, 2007.

OBJECTIVES

To assess the benefits and harms of methenamine hippurate in preventing UTI.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL in The Cochrane Library), MEDLINE (from 1950), EMBASE (from 1980), reference lists of articles and abstracts from conference proceedings without language restriction. Manufacturers' of methenamine salts were contacted for unpublished studies and contact was made with known investigators.Date of last search: June 2012

SELECTION CRITERIA

Randomised controlled trials (RCT) and quasi-RCTs of methenamine hippurate used for the prevention of UTIs in all population groups were eligible. A comparison with a control/no treatment group was a prerequisite for selection.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed study quality and extracted data. Statistical analyses were performed using the random effects model and the results expressed as risk ratio (RR) for dichotomous outcomes with 95% confidence intervals (CI). An exploration of heterogeneity and a detailed description of results, grouped by population, was undertaken.

MAIN RESULTS

Thirteen studies (2032 participants) were included. Six studies (654 patients) reported symptomatic UTI and eight studies (796 patients) reported bacteriuria. Overall, study quality was mixed. The overall pooled estimates for the major outcome measures were not interpretable because of underlying heterogeneity. Subgroup analyses suggested that methenamine hippurate may have some benefit in patients without renal tract abnormalities (symptomatic UTI: RR 0.24, 95% CI 0.07 to 0.89; bacteriuria: RR 0.56, 95% CI 0.37 to 0.83), but not in patients with known renal tract abnormalities (symptomatic UTI: RR 1.54, 95% CI 0.38 to 6.20; bacteriuria: RR 1.29, 95% CI 0.54 to 3.07). For short-term treatment duration (1 week or less) there was a significant reduction in symptomatic UTI in those without renal tract abnormalities (RR 0.14, 95% CI 0.05 to 0.38). The rate of adverse events was low.

AUTHORS' CONCLUSIONS

Methenamine hippurate may be effective for preventing UTI in patients without renal tract abnormalities, particularly when used for short-term prophylaxis. It does not appear to work in patients with neuropathic bladder or in patients who have renal tract abnormalities. The rate of adverse events was low, but poorly described.There is a need for further large well-conducted RCTs to clarify this question, particularly for longer term use for people without neuropathic bladder.

Methenamine hippurate for preventing urinary tract infections

BACKGROUND

Methenamine salts are often used as an alternative to antibiotics for the prevention of urinary tract infection (UTI). This review was first published in Issue 1, 2002 and updated in Issue 4, 2007.

OBJECTIVES

To assess the benefits and harms of methenamine hippurate in preventing UTI.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL in The Cochrane Library), MEDLINE (from 1950), EMBASE (from 1980), reference lists of articles and abstracts from conference proceedings without language restriction. Manufacturers' of methenamine salts were contacted for unpublished studies and contact was made with known investigators.Date of last search: June 2012

SELECTION CRITERIA

Randomised controlled trials (RCT) and quasi-RCTs of methenamine hippurate used for the prevention of UTIs in all population groups were eligible. A comparison with a control/no treatment group was a prerequisite for selection.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed study quality and extracted data. Statistical analyses were performed using the random effects model and the results expressed as risk ratio (RR) for dichotomous outcomes with 95% confidence intervals (CI). An exploration of heterogeneity and a detailed description of results, grouped by population, was undertaken.

MAIN RESULTS

Thirteen studies (2032 participants) were included. Six studies (654 patients) reported symptomatic UTI and eight studies (796 patients) reported bacteriuria. Overall, study quality was mixed. The overall pooled estimates for the major outcome measures were not interpretable because of underlying heterogeneity. Subgroup analyses suggested that methenamine hippurate may have some benefit in patients without renal tract abnormalities (symptomatic UTI: RR 0.24, 95% CI 0.07 to 0.89; bacteriuria: RR 0.56, 95% CI 0.37 to 0.83), but not in patients with known renal tract abnormalities (symptomatic UTI: RR 1.54, 95% CI 0.38 to 6.20; bacteriuria: RR 1.29, 95% CI 0.54 to 3.07). For short-term treatment duration (1 week or less) there was a significant reduction in symptomatic UTI in those without renal tract abnormalities (RR 0.14, 95% CI 0.05 to 0.38). The rate of adverse events was low.

AUTHORS' CONCLUSIONS

Methenamine hippurate may be effective for preventing UTI in patients without renal tract abnormalities, particularly when used for short-term prophylaxis. It does not appear to work in patients with neuropathic bladder or in patients who have renal tract abnormalities. The rate of adverse events was low, but poorly described.There is a need for further large well-conducted RCTs to clarify this question, particularly for longer term use for people without neuropathic bladder.

Diagnosis, prevention, and treatment of catheter-associated urinary tract infection in adults: 2009 International Clinical Practice Guidelines from the Infectious Diseases Society of America

Guidelines for the diagnosis, prevention, and management of persons with catheter-associated urinary tract infection (CA-UTI), both symptomatic and asymptomatic, were prepared by an Expert Panel of the Infectious Diseases Society of America. The evidence-based guidelines encompass diagnostic criteria, strategies to reduce the risk of CA-UTIs, strategies that have not been found to reduce the incidence of urinary infections, and management strategies for patients with catheter-associated asymptomatic bacteriuria or symptomatic urinary tract infection. These guidelines are intended for use by physicians in all medical specialties who perform direct patient care, with an emphasis on the care of patients in hospitals and long-term care facilities.

Methenamine hippurate for preventing urinary tract infections

BACKGROUND

Methenamine salts are often used as an alternative to antibiotics for the prevention of urinary tract infection (UTI).

OBJECTIVES

To assess the benefits and harms of methenamine hippurate in preventing UTI.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL in The Cochrane Library), MEDLINE (from 1950), EMBASE (from 1980), reference lists of articles and abstracts from conference proceedings without language restriction. Manufacturers' of methenamine salts were contacted for unpublished studies and contact was made with known investigators. Date of last search: September 2006

SELECTION CRITERIA

Randomised controlled trials (RCT) and quasi-RCTs of methenamine hippurate used for the prevention of UTIs in all population groups were eligible. A comparison with a control/no treatment group was a prerequisite for selection.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed study quality and extracted data. Statistical analyses were performed using the random effects model and the results expressed as relative risk (RR) for dichotomous outcomes with 95% confidence intervals (CI). An exploration of heterogeneity and a detailed description of results, grouped by population, was undertaken.

MAIN RESULTS

Thirteen studies (2032 participants) were included. Six studies (654 patients) reported symptomatic UTI and eight studies (796 patients) reported bacteriuria. Overall, study quality was mixed. The overall pooled estimates for the major outcome measures were not interpretable because of underlying heterogeneity. Subgroup analyses suggested that methenamine hippurate may have some benefit in patients without renal tract abnormalities (symptomatic UTI: RR 0.24, 95% CI 0.07 to 0.89; bacteriuria: RR 0.56, 95% CI 0.37 to 0.83), but not in patients with known renal tract abnormalities (symptomatic UTI: RR 1.54, 95% CI 0.38 to 6.20; bacteriuria: RR 1.29, 95% CI 0.54 to 3.07). For short-term treatment duration (1 week or less) there was a significant reduction in symptomatic UTI in those without renal tract abnormalities (RR 0.14, 95% CI 0.05 to 0.38). The rate of adverse events was low.

AUTHORS' CONCLUSIONS

Methenamine hippurate may be effective for preventing UTI in patients without renal tract abnormalities, particularly when used for short-term prophylaxis. It does not appear to work in patients with neuropathic bladder or in patients who have renal tract abnormalities. The rate of adverse events was low, but poorly described. There is a need for further large well-conducted RCTs to clarify this question, particularly for longer term use for people without neuropathic bladder.

The role of cranberry juice in the treatment of urinary tract infections

There has long been an interest in the use of cranberry, usually as a juice, to prevent and treat urinary tract infections (UTI). This mini-review examined the evidence available using a simple search on an internet-based resource designed to make evidence readily available to practitioners in the South Eastern NHS regions of the UK. The resource, known as KA24, provides access to a range of databases and full text of journal articles. The first stage of the review identified two existing Cochrane Reviews, one examining cranberry as a treatment, the other as prevention. Both concluded that there was insufficient evidence to recommend the use of cranberry in treating UTIs, although some weak research did offer support for cranberry juice in preventing UTIs. A search for further evidence not included in the Cochrane review identified several new reviews and two randomized controlled trials (RCTs) of cranberry as prevention. The reviews were not systematic and came to contradictory conclusions. They were based on a selective reading of the evidence base and gave no criteria for determining the inclusion or validity of studies. One of the RCTs was available for full scrutiny and was appraised as a valid study. Both RCTs found that cranberry (as juice or capsule) significantly reduced the rate of UTI in sexually active women. There is evidence to support the use of cranberry to prevent UTI in some populations but none to support its use as a treatment.

Methenamine hippurate for preventing urinary tract infections

BACKGROUND

Methenamine salts are often used for the prevention of urinary tract infection (UTI).

OBJECTIVES

To assess the effectiveness of methenamine hippurate in preventing UTI.

SEARCH STRATEGY

Published and unpublished randomised controlled trials were identified from the Cochrane Controlled Trials Register, MEDLINE, EMBASE, CINAHL, Current Contents, reference lists of review articles and retrieved trials. The manufacturers' of methenamine salts were contacted for unpublished studies and contact was made with known investigators in the area.

SELECTION CRITERIA

Randomised and quasi-randomised trials of methenamine hippurate used for the prevention of UTIs in all population groups were eligible for inclusion. A comparison with a control (no treatment) group was a prerequisite to selection.

DATA COLLECTION AND ANALYSIS

Two reviewers (BL and TB) performed independent assessment and data extraction using a standardised format. Discrepancies, methodological and interpretative issues were discussed with JS or JC. An exploration of heterogeneity as well as a detailed description of results grouped by population was conducted.

MAIN RESULTS

Eleven studies met the inclusion criteria. All trials were included in a descriptive analysis. Seven trials were included in meta-analyses. Four trials (199 patients) studied symptomatic bacteriuria and six trials (341 patients) studied bacteriuria as an outcome measure. Overall, trial quality was poor. The direction of six of the pooled trials was towards a favourable treatment effect from methenamine hippurate. Interpretation of the pooled estimates was not done in view of underlying heterogeneity. The study by Pettersson 1989 explained some, but not all, of the underlying heterogeneity. This study differed from all others by including patients with known upper renal tract abnormalities. Adverse reactions were mentioned by 10 studies. The rate of adverse events was low.

REVIEWER'S CONCLUSIONS

There is not enough evidence to conclusively support the use of methenamine hippurate for urinary prophylaxis. An exploration of heterogeneity raises the (hypothesis generating) possibility that methenamine hippurate may have some efficacy in patients without but not in patients with known upper renal tract abnormality (with asymptomatic bacteriuria as the outcome measure). Due to the small sample size and methodological problems within the studies involved, interpretation of these data should be done cautiously. The rate of adverse events reported by the trials was low, which suggests that current usage is unlikely to be causing significant harm.

Cranberries for treating urinary tract infections

BACKGROUND

Cranberries (particularly in the form of cranberry juice) have been used widely for several decades for the prevention and treatment of urinary tract infections. The aim of this review is to assess the effectiveness of cranberries in treating such infections.

OBJECTIVES

To assess the effectiveness of cranberries for the treatment of urinary tract infections.

SEARCH STRATEGY

The search strategy developed by the Cochrane Renal Group was used. Also, companies involved with the promotion and distribution of cranberry preparations were contacted; electronic databases and the Internet were searched using English and non English language terms; reference lists of review articles and relevant trials were also searched.

SELECTION CRITERIA

All randomised or quasi randomised controlled trials of cranberry juice or cranberry products for the treatment of urinary tract infections. Trials of men, women or children were included.

DATA COLLECTION AND ANALYSIS

Titles and abstracts of studies that were potentially relevant to the review were screened by one reviewer, RJ, who discarded studies that were clearly ineligible but aimed to be overly inclusive rather than risk losing relevant studies. Reviewers RJ and LM independently assessed whether the studies met the inclusion criteria. Further information was sought from the authors where papers contained insufficient information to make a decision about eligibility.

MAIN RESULTS

No trials were found which fulfilled all of the inclusion criteria. Two trials were excluded because they did not have any relevant outcomes.

REVIEWER'S CONCLUSIONS

After a thorough search, no randomised trials which assessed the effectiveness of cranberry juice for the treatment of urinary tract infections were found. Therefore, at the present time, there is no good quality evidence to suggest that it is effective for the treatment of urinary tract infections. Well-designed parallel group, double blind trials comparing cranberry juice and other cranberry products versus placebo to assess the effectiveness of cranberry juice in treating urinary tract infections are needed. Outcomes should include reduction in symptoms, sterilisation of the urine, side effects and adherence to therapy. Dosage (amount and concentration) and duration of therapy should also be assessed. Consumers and clinicians will welcome the evidence from these trials.

Effect of urine pH and ascorbic acid on the rate of conversion of methenamine to formaldehyde

The kinetics of conversion of methenamine to the active form formaldehyde were studied in pooled urine samples at 37 degrees in the pH range 4.9-6.5. Using a method for the determination of both formaldehyde and unhydrolyzed methenamine, the rate of formaldehyde formation in urine was found to be apparent first order and was pH dependent. Bactericidal concentrations of formaldehyde (> 28 micrograms ml-1) were achieved in 3 h in urine of pH 6.0 containing methenamine at 750 micrograms ml-1. There was no difference in the in vitro rate of conversion of methenamine to formaldehyde between the urine collected from normal subjects and the urine from subjects administered ascorbic acid. The rates of degradation of the mandelate and hippurate salts in buffer systems of various pH values did not differ significantly from those of methenamine base in urine adjusted to the same pH. The half-life of methenamine conversion to formaldehyde increased approximately 20 times from 20 h at pH 5.0 to about 400 h at pH 6.5. The data suggest that unless the urine is maintained below pH 6 only a small fraction of methenamine would be converted daily to formaldehyde and, thus, may explain the need for large doses of this drug in patients.

Anaesthesia and angiotensin-converting enzyme inhibitors. The effect of enalapril on peri-operative cardiovascular stability

The effect of enalapril pretreatment on the haemodynamic response to tracheal intubation and surgical stimulation has been studied in 22 patients. Enalapril 5 mg given 4 hours before operation was associated with a significant reduction in the pressor response associated with intubation (p less than 0.05) and surgical stimulation (p less than 0.005) compared with control. Heart rate changes were similar in the two groups. The role of the renin-angiotensin system in relation to the pressor response to sympathetic stimulation is discussed and it is concluded that angiotensin-converting enzyme inhibitors may help improve peri-operative cardiovascular stability.