Methenamine mandelate with acidification: an effective urinary antiseptic in patients with neurogenic bladder

Treatment of Recurrent Urinary Tract Infection Symptoms with Urinary Antiseptics Containing Methenamine and Methylene Blue: Analysis of Etiology and Treatment Outcomes

Purpose

Urinary antiseptics including methenamine and methylene blue are used in the symptomatic treatment of urinary tract infections (UTIs).

Patients and Methods

This was a prospective, double-blind, randomized, double-dummy safety and efficacy study of 2 urinary antiseptic combinations in the symptomatic treatment of recurrent cystitis: methenamine 120mg + methylene blue 20mg (Group A) versus acriflavine 15mg + methenamine 250mg + methylene blue 20mg + Atropa belladonna L. 15mg (Group B). All subjects underwent pretreatment urine culture and antibiotic sensitivity tests prior to 3-day oral treatment with study drug, followed by 3 days of antibiotic therapy (based on urine culture) + study drug treatment. Efficacy was evaluated using the Urinary Tract Infection Symptoms Assessment Questionnaire (UTISA). The primary endpoint was the percentage of patients presenting improvement in cystitis manifestations on the UTISA domain "Urination Regularity" at Visit 2. The primary safety variable was the incidence of treatment-related adverse events.

Results

A total of 144 subjects were randomized per group and 272 completed the study. Primary endpoint analysis demonstrates homogeneity between treatment groups, with 69.4% and 72.2% subjects, respectively, showing improvement in the score of the urinary regularity UTISA domain after 3 days of treatment (p= 0.87). At Visit 2, incidence of treatment-related adverse events was higher in Group B (Group A: n= 11, Group B: n= 31, p= 0.0057).

Conclusion

Both treatments were effective in reducing UTI symptoms assessed by UTISA questionnaire after 3 days of treatment. The two regimens were comparable in incidence of adverse events, but the combination of methenamine + methylene blue resulted in fewer treatment-related adverse effects.

The relationship of seasonality and the increase in urinary tract infections among hospitalized patients with spinal cord injury

BACKGROUND

Urinary tract infection (UTI) is the most frequent complication in patients who have spinal cord injury (SCI). The occurrence rate of UTI in this type of hospitalized patients was correlated to seasonality, age, and gender.

METHODS

Patients hospitalized during the 4-year study period with underlying SCI were identified from Taiwan's National Health Insurance Research Database. Patients with a discharge diagnosis of UTI were identified as those with SCI and UTI; they were divided into the following four age groups: <18 years, 18 to 44 years, 45 to 64 years, and ≥65 years. The gender, monthly number of cases, major complication rate, seasonal differences, and odds ratios (ORs) of associated factors were analyzed.

RESULTS

Data of 30 149 hospitalized patients diagnosed with SCI were retrieved. SCI and UTI were diagnosed in 3405 (11.3%) patients, of them 2296 were males (67.4%) and 1109 were females (32.6%). The UTI occurrence rate in hospitalized SCI patients was higher in males (11.8%) than in females (10.4%) (OR: 1.24; 95% CI: 1.15-1.34); it was highest in the ≥65-year-old age group (12.8%) and lowest in the <18-year-old age group (5.8%) (OR: 2.51; 95% CI: 1.83-3.44). The UTI occurrence rate varied from 7% to 18%, and it was highest in the summer (13.0% ± 2.6%) and lowest in the winter (10.2% ± 1.9%) (OR: 1.27; 95% CI: 1.15-1.40). Acute pyelonephritis was the most common complication in SCI and UTI cases.

CONCLUSION

The mean occurrence rate of UTI in hospitalized SCI patients was 11.3%; it was higher in males, in patients aged ≥65 years, and in the summer. Therefore, physicians should pay attention to the occurrence of UTI in aged male patients with SCI, especially in the summer.

Catheter-associated urinary tract infections in persons with neurogenic bladders

This review is based on the author's Donald Munro Lecture given at the annual conference of the Academy of Spinal Cord Injury Professionals in New Orleans, LA. Indwelling catheters play an important role in bladder management following SCI for many individuals with neurogenic bladders. There is an increased risk of UTI compared to other types of bladder management with indwelling urethral catheters but not SP catheters. To minimize the risk of symptomatic UTI, the following steps are essential: prevent bladder wall distention and resulting ischemia, maintain colonization with "good" bacteria, and prevent bladder stones. For individuals with recurrent symptomatic UTIs, try to change the environment, prevent bladder over distention, and make sure the bladder is "quiet" by using strategies such as adequate dosages of anticholinergics, onabotulinum toxin A, and preventing catheter blockage. Bacterial colonization of the bladder is common. However, bacterial colonization may have a positive effect by inhibition of colonization of pathogenic bacteria. Judicious use of antibiotics is important since antibiotics hasten the evolution of more resistant organisms. Potential prevention and treatment strategies include killing the offending organisms, changing the environment (such as urinary acidification), and modifying virulence factors and the bacterial microbiome.

A pH-sensitive methenamine mandelate-loaded nanoparticle induces DNA damage and apoptosis of cancer cells

Methenamine mandelate is a urinary antibacterial agent, which can be converted to formaldehyde in urine that has a relatively low pH of average 5.5-6.8. Here, we prepare a pH-sensitive PLGA-based nanoparticle containing both methenamine mandelate and NaHCO₃. Methenamine mandelate/NaHCO₃-coloaded nanoparticle could enter cells via endosome/lysosome pathway. The pH in lysosomes and endo-lysosomes is approximately 5.0. In the acidic environment, NaHCO₃ reacts with proton and produce CO₂ bubbles, which burst nanoparticles and lead to the rapidly release of methenamine mandelate. Meanwhile, methenamine mandelate was then quickly converted to a sufficient amount of formaldehyde in this acidic environment, which induced DNA damage and DNA damage response (DDR). Consequently, methenamine mandelate/NaHCO₃-coloaded nanoparticles caused cell cycle arrest, cell growth inhibition and apoptosis of cancer cells. Moreover, methenamine mandelate/NaHCO₃-coloaded nanoparticles also show intensive inhibitory effect on the growth of MCF-7 xenograft tumor in vivo. Therefore, methenamine mandelate/NaHCO₃-coloaded nanoparticle is a promising type of formulation for the treatment of cancer, which could give the "old drug" methenamine mandelate a new anti-cancer function in clinical.

STATEMENT OF SIGNIFICANCE

Methenamine mandelate is a urinary antibacterial agent, which can be converted to formaldehyde in urine that has a relatively low pH of average 5.5-6.8. Here, we prepare a pH-sensitive PLGA-based nanoparticle containing both methenamine mandelate and NaHCO₃. Methenamine mandelate/NaHCO₃-coloaded nanoparticle could enter cells via endosome/lysosome pathway. The pH in lysosomes and endo-lysosomes is approximately 5.0. In the acidic environment, NaHCO₃ reacts with proton and produce CO₂ bubbles, which burst nanoparticles and lead to the rapidly release of methenamine mandelate. Meanwhile, methenamine mandelate was then quickly converted to a sufficient amount of formaldehyde in this acidic environment, which induced DNA damage and DNA damage response (DDR). Methenamine mandelate/NaHCO₃-coloaded nanoparticle is a promising type formulation for the treatment of cancer, which could give the "old drug" methenamine mandelate a new anti-cancer function in clinical.

Gentamicin bladder instillations decrease symptomatic urinary tract infections in neurogenic bladder patients on intermittent catheterization

INTRODUCTION

This study aimed to determine if gentamicin bladder instillations reduce the rate of symptomatic urinary tract infection (UTI) in neurogenic bladder (NGB) patients on intermittent self-catheterization (ISC) who have recurrent UTIs. Secondary aims were to examine the effects of intravesical gentamicin on the organism resistance patterns.

METHODS

We retrospectively reviewed our prospective NGB database. Inclusion criteria were NGB patients performing ISC exclusively for bladder drainage with clinical data available for six months before and six months after initiating prophylactic intravesical gentamicin instillations. Symptomatic UTIs were defined as symptoms consistent with UTI plus the need for antibiotic treatment.

RESULTS

Twenty-two patients met inclusion criteria; etiology of NGB was 63.6% spinal cord injury, 13.6% multiple sclerosis. Median time since injury/diagnosis was 14 years and 6/22 (27.3%) had undergone urological reconstruction. Patients had fewer symptomatic UTI's (median 4 vs. 1 episodes; p<0.004) and underwent fewer courses of oral antibiotics after initiating gentamicin (median 3.5 vs. 1; p<0.01). Days of oral antibiotic therapy decreased from 15 before to five after gentamicin, but this did not reach significance. There were fewer telephone encounters for UTI concerns per patient (median 3 vs. 0; p=0.03). The proportion of multi-drug-resistant organisms in urine cultures decreased from 58.3% to 47.1% (p=0.04) and the rate of gentamicin resistance did not increase. Adverse events were mild and rare.

CONCLUSIONS

Gentamicin bladder instillations decrease symptomatic UTI episodes and reduce oral antibiotics in patients with NGB on ISC who were suffering from recurrent UTIs. Antibiotic resistance decreased while on gentamicin instillations.

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.

Intermittent catheterization and recurrent urinary tract infection in spinal cord injury

PURPOSE

To study the association of recurrent symptomatic urinary tract infections (UTIs) with the long-term use of clean intermittent catheterization (CIC) for the management of neurogenic bladder in patients with spinal cord injury (SCI).

METHODS

Retrospective study of 61 SCI patients with neurogenic bladder managed by CIC. Subjects were selected from 210 SCI patients seen at the Yale Urology Medical Group between 2000 and 2010. Medical UTI prophylaxis (PRx) with oral antimicrobials or methenamine/ascorbic acid was used to identify patients with recurrent UTI. The number of positive cultures (≥10(3) cfu/mL) within a year prior to starting PRx was used to confirm the recurrence of UTI.

RESULTS

Fifty-one male and 10 female subjects were managed with CIC. Forty-one (67%) subjects were placed on medical PRx for symptomatic recurrent UTI. Seventeen (28%) subjects had at least 3 positive cultures within the year prior to starting PRx. Fifteen of 20 (75%) subjects not on PRx had no complaints of UTI symptoms in the final year of follow-up.

CONCLUSION

Recurrent symptomatic UTIs remain a major complication of long-term CIC in SCI patients. Although CIC is believed to have the fewest number of complications, many SCI patients managed with long-term CIC are started on medical PRx early in the course of management. Future studies are needed to determine the efficacy of routine UTI PRx in these patients as well as determine what factors influence why many patients on CIC experience frequent infections and others do not.

Urine antibiotic activity in patients presenting to hospitals in Laos: implications for worsening antibiotic resistance

Widespread use of antibiotics may be important in the spread of antimicrobial resistance. We estimated the proportion of Lao in- and outpatients who had taken antibiotics before medical consultation by detecting antibiotic activity in their urine added to lawns of Bacillus stearothermophilus, Escherichia coli, and Streptococcus pyogenes. In the retrospective (N = 2,058) and prospective studies (N = 1,153), 49.7% (95% confidence interval [CI] = 47.4–52.0) and 36.2% (95% CI = 33.4–38.9), respectively, of Vientiane patients had urinary antibiotic activity detected. The highest frequency of estimated antibiotic pre-treatment was found in patients recruited with suspected central nervous system infections and community-acquired septicemia (both 56.8%). In Vientiane, children had a higher frequency of estimated antibiotic pre-treatment than adults (60.0% versus 46.5%; P < 0.001). Antibiotic use based on patients histories was significantly less frequent than when estimated from urinary antibiotic activity (P < 0.0001).

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.

Complications of intermittent catheterization: their prevention and treatment

STUDY DESIGN

Literature review to evaluate the complications seen in patients on intermittent catheterization (IC) and intermittent self-catheterization (ISC).

OBJECTIVES

To find the prevalence of most complications seen in patients on IC. To study the prevention and the treatment of these complications.

SETTING

An international literature review.

METHODS

Most relevant articles on the subject are reviewed.

CONCLUSION

Urinary tract infection is the most frequent complication in patients performing IC. Catheterization frequency and the avoidance of bladder overfilling are amongst the most important prevention measures. Asymptomatic bacteriuria does not need to be treated with antibiotics. Long-term antibacterial prevention does seem to bear a risk of development of bacterial resistance. Previous treatment with indwelling catheters is a risk factor for chronic infection and urinary sepsis. Prostatitis is more frequently present than often thought. Epididymitis and urethritis are rare. Trauma from catheterization occurs regularly, but lasting effects are more limited. However, the prevalence of urethral strictures and false passages increases with longer use of IC. The use of hydrophilic catheters might be able to lower the urethral complication rate but additional proof through comparative studies is needed. The most important prevention measures are good education of all involved in IC, good patient compliance, the use of a proper material and the application of a good catheterization technique.

Urinary tract infections in patients with spinal cord lesions: treatment and prevention

Even though the mortality due to urinary tract complications has decreased dramatically during the last decades in individuals with spinal cord lesions (SCL), urinary tract infections (UTI) still cause significant morbidity in this population. Complicated UTI are caused by a much wider variety of organisms in individuals with SCL than in the general population and are often polymicrobial. Escherichia coli, Pseudomonas spp., Klebsiella spp., Proteus spp., Serratia spp., Providencia spp., enterococci, and staphylococci are the most frequently isolated bacteria in urine specimens taken from individuals with SCL. There is no doubt that the greatest risk for complicated UTI in these individuals is the use of an indwelling catheter. Intermittent catheterisation during the rehabilitation phase has been shown to lower the rate of UTI, and virtually eliminate many of the complications associated with indwelling catheters. Persons with SCL should only be treated for bacteriuria if they have symptoms. Generally, it is advisable to use antibacterial agents with little or no impact on the normal flora. Single agent therapy - in accordance with antimicrobial susceptibility test - is preferred. We advise extending treatment to at least 5 days, and in those with reinfection or relapsing UTI, at least 7 to 14 days, depending on the severity of the infection. The diagnosis of structural and/or functional risk factors is essential in order to plan an optimal treatment for UTI in individuals with SCL, which should include treatment of simultaneously occurring predisposing factors. The treatment of structural risk factors follows general urological principles, aiming for sufficient outlet from the bladder with minimal residual urine and low pressure voiding. For prevention of UTI, general cleanliness and local hygiene should be encouraged. If the patient has a reinfection or relapsing symptomatic UTI, it is important to check for inadequately treated infection and complications, which need special attention, in particular residual urine and urinary stones. No reliable evidence exists of the effectiveness of cranberry juice and other cranberry products. Prophylactic antibacterials should only be used in patients with recurrent UTI where no underlying cause can be found and managed, and in particular if the upper urinary tract is dilated. Antibacterials should not be used for the prevention of UTI in individuals with SCL and indwelling catheters. However, the use of prophylactic antibacterials for individuals with SCL using intermittent catheterisation or other methods of bladder emptying is controversial.

Antimicrobial prophylaxis for urinary tract infection in persons with spinal cord dysfunction

OBJECTIVE

To assess the benefits and harms of antimicrobial prophylaxis to prevent urinary tract infections (UTIs) in persons with neurogenic bladders caused by spinal cord dysfunction.

DATA SOURCES

A broad search strategy with no language restriction was conducted of MEDLINE (1966-January 1998), EMBASE (1974-January 1998), and CINAHL (1982-July 1998) using the general search terms urinary tract, urinary tract infections, bacteriuria, paraplegia, quadriplegia, spinal cord injuries, multiple sclerosis, neurogenic bladder, and neuropathic bladder. Additional articles were identified by experts and by reviewing reference lists of articles obtained from searches.

STUDY SELECTION

Criteria included human studies of adults and adolescents who had neurogenic bladder due to spinal cord dysfunction; the studies had to address antimicrobial prophylaxis of UTI and include bacteriuria or UTI as an outcome. We excluded any study that was clearly not a controlled trial or that only included children under the age of 13 years. Two reviewers independently abstracted data, and disagreements were resolved by consensus.

DATA EXTRACTION

Two reviewers independently abstracted data, and disagreements were resolved by consensus. Studies were graded by 1 project investigator according to quality criteria developed by Jadad and Schulz.

DATA SYNTHESIS

The sizes of the effect of antimicrobial prophylaxis on weekly infection rates from 15 trials that met the inclusion criteria were pooled by using a random effects model. Antimicrobial prophylaxis did not significantly decrease symptomatic infections. Prophylaxis was associated with a reduction in asymptomatic bacteriuria among acute patients (<90d after spinal cord injury; P <.05); 1 patient would require 3.7 weeks of treatment on average to prevent 1 asymptomatic infection. For nonacute patients, the reduction approached statistical significance (P =.06). Prophylaxis resulted in an approximately twofold increase in antimicrobial-resistant bacteria.

CONCLUSIONS

The regular use of antimicrobial prophylaxis for most patients who have neurogenic bladder caused by spinal cord dysfunction is not supported. A clinically important effect, however, has not been excluded. Future research should focus on randomized trials in those patients who have recurrent UTIs that limit their daily functioning and well-being.

Catheter-associated urinary tract infections

Millions of urethral catheters are used each year. This device subverts several host defenses to allow bacterial entry at the rate of 3% to 10% incidence per day, and its presence encourages the organism's persistent residence in the urinary tract. Most catheter-associated bacteriurias are asymptomatic. The complications in short-term catheterized patients include fever, acute pyelonephritis, bacteremia, and death; patients with long-term catheters in place are at risk for these complications and catheter obstruction, urinary tract stones, local periurinary infections, chronic renal inflammation, chronic pyelonephritis, and, over years, bladder cancer. The closed catheter system has been a magnificant step forward in the prevention of catheter-associated bacteriuria. Indeed, only two catheter principles are universally recommended: keep the closed catheter system closed and remove the catheter as soon as possible. Most modifications of the closed catheter system have not improved markedly on its ability to postpone bacteriuria. On first inspection, systemic antibiotics seem to be an exception to this rule, but their use results in infection of the bladder with resistant organisms, including candida. This and the effect of side effects on the patient and emergence of resistant bacteria in the medical unit have led most authorities to conclude that antibiotics are not useful for prevention of bacteriuria, nor for treatment of bacteriuria in the asymptomatic catheterized patient. For symptomatic patients, usually with fever or signs of sepsis, treatment of bacteriuria with appropriate systemic antibiotics and removal or replacement of the urethral catheter are indicated. Gloves, hand washing, and segregation of catheterized patients can minimize nosocomial clusters. Because clinicians can only postpone bacteriuria, and once it occurs, clinicians seem unable to prevent its complications, methodologies other than urethral catheters should be used for urine drainage assistance whenever possible. These options include condom, intermittent, suprapubic, and intraurethral catheterization for appropriate patients. The few data available suggest that each one of these catheterization options yields a lower incidence of bacteriuria-and its consequent complications-than urethral catheterization.

Trimethoprim-sulfamethoxazole prophylaxis against urinary tract infection in the chronic spinal cord injury patient

Suppressive therapy with antibiotics has long been thought to decrease the number of complications from the neuropathic bladder in spinal cord injury patients, but it may also induce resistance to antibiotics which subsequently causes difficulties in treating symptomatic urinary tract infections. Forty-three chronic spinal cord injury patients were randomized to continue to receive daily trimethoprim-sulfamethoxazole (TMP-SMX) urinary tract prophylaxis versus discontinuing antibiotic prophylaxis. Patients were all at least 6 months after spinal cord injury. Patients were followed for a minimum of 3 months, with weekly catheter urine cultures. The difference in the colonization rate at onset and after 3 months (percent of cultures with asymptomatic bacteriuria) between the control and prophylaxis group was not statistically significant (P > 0.1). There was a significant decrease in the percentage of TMP-SMX resistant asymptomatic bacteriuria in the control group, 78.8%, compared to 94.1% in the suppressive group (P < 0.05). There was no significant difference in the number of symptomatic urinary tract infections following the withdrawal of suppressive therapy between the control group, 0.035/week, and the prophylaxis group, 0.043/week (P > 0.5). There was a larger percentage of TMP-SMX resistant symptomatic urinary tract infections in the treated group, 42.5% versus 37.5% in the control group, but the difference was not significant (P > 0.5). Irrespective of the method of bladder management, suppressive therapy with TMP-SMX did not reduce the incidence of symptomatic bacteriuria and did increase the percentage of cultures resistant to TMP-SMX in asymptomatic patients.

Prophylaxis of urinary tract infection in persons with recent spinal cord injury: a prospective, randomized, double-blind, placebo-controlled study of trimethoprim-sulfamethoxazole

PURPOSE

To determine the efficacy of trimethoprim-sulfamethoxazole (TMP-SMX) for prophylaxis of urinary tract infection in persons with recent spinal cord injury, during the first 4 months of intermittent catheterization.

PATIENTS AND METHODS

One hundred twenty-nine adults (112 men, 17 women) with recent acute spinal cord injury participated in a randomized, double-blind, placebo-controlled trial, and were studied for up to 16 weeks. Low-dose TMP-SMX (TMP 40 mg, SMX 200 mg) or placebo was given once daily. Clinical observations, urine cultures, and cultures of rectal and urethral swabs were made weekly. Subjects who developed breakthrough bacteriuria received conventional antimicrobial therapy and prophylaxis was continued.

RESULTS

Sixty-six TMP-SMX recipients (57 men, 9 women) and 60 placebo recipients (52 men, 8 women) are evaluable for efficacy. Among male subjects, bacteriuria was present during 50% or more of study weeks in 30% of TMP-SMX recipients and in 56% of placebo recipients (p = 0.003). The interval to the onset of bacteriuria was prolonged in TMP-SMX recipients (p < 0.0001). TMP-SMX recipients without bacteriuria in any given week had a lower probability of having bacteriuria the subsequent week (0.26) than did placebo recipients (0.49) (p < 0.0001). At least 1 episode of definite symptomatic bacteriuria (bacteriuria and fever and at least 1 classical manifestation of urinary infection) occurred in 4 of 57 TMP-SMX-treated men and in 18 of 52 placebo-treated men (p < 0.0003). We observed similar trends in women, but differences did not reach statistical significance, perhaps because the number of females was small. Adverse events suspected to be due to medications were frequent in this population of patients with recent severe injuries and led to discontinuation of the study in 10% of the TMP-SMX group and 8% of the placebo group. Adverse events included neutropenia (TMP-SMX: two; placebo: three), pseudomembranous colitis (TMP-SMX: one), severe skin rash (TMP-SMX: two; placebo: one), and drug fever (TMP-SMX: one). The proportion of all episodes of bacteriuria that were due to TMP-SMX-resistant organisms was unexpectedly high in the placebo group (51%), and increased progressively according to year of enrollment in the study. By Year 3, all subjects in the placebo group had at least one episode of TMP-SMX-resistant bacteriuria. Gram-negative enteric bacilli resistant to TMP-SMX were recovered from rectal swabs (TMP-SMX 49%, placebo 42%) and urethral swabs (TMP-SMX 33%, placebo 26%) in similar proportions of subjects in the two study groups.

CONCLUSIONS

Prophylaxis with TMP-SMX significantly reduces bacteriuria and symptomatic urinary tract infection in persons with recent acute spinal cord injury during bladder retraining using intermittent catheterization. However, adverse reactions attributable to TMP-SMX are common in this population. Colonization and breakthrough bacteriuria with TMP-SMX-resistant organisms are frequent and may seriously limit the usefulness of this strategy, particularly in an institutional setting.

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.

Prophylactic antibacterial therapy for preventing urinary tract infections in spinal cord injury patients

We conducted 202 trials in 161 male hospital patients to determine if prophylactic administration of ascorbic acid or antibacterials (trimethoprim-sulfamethoxazole, nalidixic acid, methenamine hippurate or nitrofurantoin macrocrystals) would prevent bacteriuria infections in spinal cord injury patients who had had at least 1 bout of bacteriuria. None of the drugs tested appeared to be statistically effective in the doses used in preventing bacteriuria in these patients. Moreover, sensitivities were lost to several drugs other than those used prophylactically. We conclude that use of prophylactic doses of ascorbic acid or antibacterials has not proved to be beneficial in spinal cord injury patients free of indwelling catheters.