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At least 19 recordsLinked to original sources
PubMed2005

Determination of methenamine, methenamine mandelate and methenamine hippurate in pharmaceutical preparations using ion-exchange HPLC.

An ion-exchange column high-performance liquid chromatography (HPLC) method has been developed for the determination of methenamine in methenamine and methenamine hippurate pharmaceutical preparations. The HPLC method uses a Zorbax SCX-300 column with acetonitrile-0.1M sodium perchlorate monohydrate (pH 5.8) (70:30, v/v) as the mobile phase at the flow rate of 1 mL/min. UV-detection was at 212 nm. The linear concentration plots for methenamine were linear over the concentration range of 0.25-50mM for methenamine and methenamine mandelate standards. The intra-day RSD precision was <1.25%, and for inter-day, <1.85%. The peaks for mandelic acid, hippuric acid and the other ingredients from placebo tablets do not interfere with the analysis for methenamine. The accuracy of this method was shown to be 99-101% by measuring the recovery of methenamine from spiked placebo tablets. The assay of methenamine from methenamine hippurate tablets and from a urinary antiseptic tablet containing methenamine were in the range of 98-102%. This HPLC method is a fast, simple and straightforward method for the analysis of methenamine in pharmaceutical preparations.

Anti-Infective Agents, Urinary↗
PubMed1981

Urinary excretion of methenamine and formaldehyde: evaluation of 10 methenamine products in humans.

The urinary excretion of both methenamine and formaldehyde was measured for 48 hr after the oral administration of 10 different methenamine products to 10 human subjects in a crossover study. The following dosage forms were evaluated: a tablet of methenamine base, a methenamine hippurate tablet, and eight products containing methenamine mandelate, including six enteric-coated tablets, a suspension, and a granule dosage form. The nonenteric-coated dosage forms were absorbed more rapidly, based on maximum excretion rates that occurred within 3 hr after dosing. The enteric-coated tablets, which were designed not to release methenamine until reaching the intestinal tract, exhibited maximum excretion rates that did not occur until 7-17 hr after dosing. There were no significant differences (p greater than 0.05) among products in terms of total excretion of free formaldehyde in the urine. However, large differences (p less than 0.05) were noted among products for urinary recovery of total methenamine, with the amount of administered dose recovered ranging from 16 to 83%.

Adult↗
PubMedDate not supplied

Simultaneous determination of methenamine and formaldehyde in the urine of humans after methenamine administration.

Methenamine (hexamethylenetetramine) and its hydrolysis product formaldehyde are determined in the presence of each other in urine by a spectrophotometric method. Formaldehyde is assayed by a colour reaction with tryptophan, sulphuric acid and ferric chloride after precipitating methenamine by three treatments with mercuric chloride. Methenamine is indirectly analysed by hydrolysis to formaldehyde with dilute hydrochloric acid. Formaldehyde levels as low as 5.0 micrograms ml-1 in the presence of methenamine concentrations as high as 2.5 mg ml-1 can be assayed. Of practical significance is the feature that urine may be stored up to 1 weeks for analysis, by appropriate dilution and freezing, without excessive loss of methenamine or formaldehyde. The method was applied to the dtermination of the bioavailability of methenamine hippurate in ten human volunteers.

Biological Availability↗
PubMed1979

Drug therapy reviews: methenamine mandelate and methenamine hippurate.

The mechanism of action, spectrum of antimicrobial activity, pharmacokinetics, adverse effects, therapeutic use, and dosage of methenamine hippurate and methenamine mandelate are reviewed. The antimicrobial activity of methenamine depends on its conversion in the urine to formaldehyde. Formaldehyde's spectrum of antibacterial activity encompasses all urinary tract pathogens. Urinary concentrations of formaldehyde vary with pH and urine volume; however, there is no documentation that acdification of the urine enhances methenamine's therapeutic activity. Adverse reactions to methenamine, including gastrointestinal intolerance and skin reactions, are mild and reversible and occur infrequently. Methenamine mandelate and hippurate are effective in the prevention of recurrent urinary tract infections except in patients with Foley catheters or who require intermittent catheterization.

Bacteria↗
PubMed1979

Biological fate of methenamine in man. Absorption, renal excretion and passage to umbilical cord blood, amniotic fluid and breast milk.

Methenamine hippurate was administered orally as tablets or granules to healthy volunteers. Plasma concentrations of methenamine reached a maximum 1--2 hours after a single dose and then declined with a half-life of about 4 hours. The apparent distribution volume was similar to that of total body water. Renal clearance of methenamine was somewhat lower than that of creatinine. In cross-over experiments over six days, methenamine recovered in the urine corresponded to about 80 per cent of the dose given per 12 hours, slightly lower values being obtained from granules than from tablets. The efficient renal elimination of methenamine was confirmed in similar studies on patients post-operatively. Methenamine hippurate was also given to healthy pregnant women during labor, a few hours before expected delivery. Methenamine was found to pass the placental barrier. The concentration of methenamine in umbilical cord plasma was low but reached the level in maternal plasma after about 4 hours. In amniotic fluid the methenamine con centration was low and varying. No correlation was obtained to the maternal or umbilical cord plasma levels. The methenamine concentration in breast milk was of the same magnitude as in maternal plasma. It is concluded that methenamine may be safely given to pregnant and lactating women with respect to the ellbeing of the child.

Absorption↗
PubMed1986

Separation and quantitation of methenamine in urine by ion-pair extraction.

An ion-pair extraction technique is described for separating methenamine, a urinary tract antibacterial agent, from formaldehyde in human urine samples. Separation conditions are developed from extraction constants for the methenamine-bromocresol green ion-pair. The technique involves adsorption of the ion-pair onto a silica cartridge and elution with methylene chloride:1-pentanol (95:5). Methenamine is freed from the ion-pair by the addition of excess tetrabutylammonium iodide and converted to formaldehyde (determined spectrophotometrically) by reaction with ammonia and acetylacetone. Linear standard plots were obtained from urine containing methenamine which was diluted to 10-160 micrograms/mL. The lower limit of detection was 6 micrograms/mL of methenamine. Absolute recovery from urine was greater than or equal to 94.5%. The precision (CV) of detection of methenamine in the presence of formaldehyde was less than 2%, and less than or equal to 4.5% for the detection of formaldehyde in the presence of methenamine. No interferences were noted. The applicability of the method was demonstrated by analysis of human urine levels of both methenamine and formaldehyde following oral administration of a methenamine salt to a volunteer.

Adult↗
PubMed1998

Capillary gas chromatographic assay of residual methenamine hippurate in equipment cleaning validation swabs.

A capillary gas chromatographic method is described for the determination of methenamine hippurate residue in swabs collected from manufacturing equipment surfaces. Any residual methenamine hippurate remaining on process equipment after cleaning is removed by swabbing with one wet polyester Absorbond swab (4" x 4") pre-moistened with water followed by a dry Absorbond swab. The residual methenamine hippurate is chromatographed on a 30 x 0.32 mm (i.d.) Supelcowax-10 capillary column of 0.25-micron film thickness. The amount of residual methenamine hippurate is determined by comparing the ratio of methenamine hippurate peak area response to that of p-cresol (internal standard) obtained for the sample to a linear calibration curve obtained for a series of standard solutions. The method is demonstrated to be sufficiently linear, accurate, precise, sensitive and rugged for the determination of low levels of methenamine hippurate on equipment surfaces. Using this method, the mean recovery of methenamine hippurate from spiked Absorbond swab samples contained in high density polyethylene bottles was 105.2%, with a relative standard deviation (RSD) of +/- 7.1% (n = 25). The mean recoveries of methenamine hippurate from spiked test plates for '180 Grit' Stainless Steel, Teflon and WARCO White (neoprene and PVC) gasket material were 77.2, 96.1 and 50.6%, with RSDs of +/- 9.4 (n = 25), +/- 4.3 (n = 25) and +/- 36% (n = 20), respectively. Recovery correction factors have been incorporated into the method. The method was successfully applied to the assay of actual equipment cleaning validation swab samples. Stability studies demonstrate that methenamine hippurate is not very stable on the equipment surfaces or in the swabs. It is recommended that the surfaces be swabbed immediately after cleaning and the swabs analyzed within 24 h after sample collection. The results demonstrate that in order to fully validate the cleaning procedures, it is not only necessary to investigate the recovery of the drug from equipment surfaces and swabs but also that the stability of the drug on the surfaces and swabs be determined.

Anti-Infective Agents, Urinary↗
PubMed1984

Formaldehyde generation from methenamine salts in spinal cord injury.

To achieve effective suppression of bacteriuria in spinal cord injured (SCI) patients, methenamine mandelate and methenamine hippurate are commonly given with ascorbic acid. Since the effectiveness of ascorbic acid as a urinary acidifier has been challenged and as it also has been suggested that methenamine salts do not produce effective urine formaldehyde concentrations in patients with indwelling urethral catheters, we studied two groups of SCI patients to determine (1) the effect of ascorbic acid on urine pH and formaldehyde concentration when administered with methenamine salts; (2) the effect of an indwelling urethral catheter versus intermittent catheterization on formaldehyde concentration in the urine of SCI patients taking methenamine salts; and (3) the relative urine formaldehyde concentrations produced by treatment with methenamine mandelate and methenamine hippurate in SCI patients. Methenamine mandelate produced significantly higher urine formaldehyde concentrations than did methenamine hippurate, especially among patients with intermittent catheterization. Ascorbic acid produced a significant effect on urine pH but not on formaldehyde concentration.

Anti-Infective Agents, Urinary↗
PubMed2002

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.

Anti-Infective Agents, Urinary↗
PubMed1993

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.

Anti-Infective Agents, Urinary↗
PubMed2002

Primary evaluation of methenamine as a NPN compound with probable effects on increasing ruminal escaped protein.

The effects of methenamine as a non-protein nitrogenous compound on protein and health status of feedlot lambs were studied in three groups of lambs receiving 5, 10, or 15 g of the substance daily in their feed for 100 days. The results were compared with data obtained from a control group receiving a diet low in crude protein without methenamine. Serum total protein, serum urea nitrogen and serum creatinine were measured every 10 days as indicators of protein metabolism and kidney function. Urine samples were also examined on the same days for possible side-effects of methenamine on the urinary tract. Following slaughter, various internal organs, including the brain and various parts of the gastrointestinal and urinary tracts, were examined both grossly and microscopically to detect any lesions. All groups receiving methenamine had serum total protein and serum urea nitrogen levels higher than those in the control group. The serum creatinine level was normal in all the groups throughout the experiment. No gross or microscopic lesion attributed to the toxic effects of methenamine was detected in any of the internal organs. Therefore, it is concluded that methenamine can be used as a non-protein nitrogenous compound without serious side-effects.

Animal Nutritional Physiological Phenomena↗
PubMedDate not supplied

Long-term treatment with methenamine hippurate in recurrent urinary tract infection.

Twenty-four patients with a history of recurrent urinary tract infection and in whom residual urine was considered to be a factor of importance for chronicity, have been treated for an average of 16 months with 1 g methenamine hippurate morning and evening. No patient had urinary calculus at the commencement of treatment and neither did any patient have an indwelling catheter. In patients without urinary tract infection or in whom abacteriuria was achieved with methenamine hippurate, the number of reinfections was reduced by approximately two thirds compared to periods prior to treatment. No patient was completely free from infection throughout the whole treatment period. However, in no case did bacteria with extensive resistance appear. When urinary tract infection was treated with methenamine hippurate, abacteriuria was achieved in only 6 of 14 patients. It would therefore seem that this agent is only of limited value for treatment of established infection. In the event of manifest infection it would appear appropriate to treat the infection primarily with antibiotics and to use methenamine hippurate for prophylaxis when abacteriuria has been achieved. No patient developed urinary calculus during treatment with methenamine hippurate and no deterioration of renal function or haematological change was observed.

Adult↗
PubMed1979

Appraisal of ascorbic acid for acidifying the urine of methenamine-treated geriatric patients.

A study was made of 73 elderly patients receiving methenamine and ascorbic acid concurrently. Each patient had an indwelling Foley catheter. Urinary pH was assessed in relation to the dosage of ascorbic acid, duration of therapy, formulation, and dosing intervals for ascorbic acid and methenamine. Statistical analysis revealed a significant increase in urinary pH when the dosage of ascorbic acid was increased. No significant relationships were found between urinary pH and the dosage forms of ascorbic acid, the salt of methenamine used, or the duration of methenamine therapy. Changes in urinary pH at different dosing intervals for ascorbic acid were found to be significant, at the 10 percent level only, for the three-times-daily dose schedule. These data raise a question as to the value of ascorbic acid for acidifying the urine of catheterized patients receiving methenamine therapy.

Aged↗
PubMed1987

Prevention of recurrent acute cystitis by methenamine hippurate: double blind controlled crossover long term study.

In a randomised, double blind, long term, crossover study 1 g twice daily of methenamine hippurate was compared with placebo for its preventive effect on recurrent attacks of acute cystitis. Methenamine hippurate and placebo were interchanged every six months for two years. During one of the years patients took 250 ml extra fluid every morning and evening. Out of 21 enrolled patients, 14 completed the first year and 13 both years of treatment, which permitted the evaluation of 27 patient years. There were 52 episodes of acute cystitis caused by reinfection: 41 occurred during placebo treatment and only 11 during the methenamine hippurate regimen (p less than 0.01). Extra fluid intake did not reduce the incidence of acute cystitis, nor did it reduce the effect of methenamine hippurate. Methenamine hippurate is an effective prophylactic agent against recurrent acute cystitis and has the advantage of not inducing cross resistance to conventional antibiotics.

Acute Disease↗
PubMed1983

Conductometric determination of methenamine.

A method of conductometric titration for determination of methenamine is presented. An aqueous solution of silicotungstic acid is used as titrant. The acid and methenamine form an insoluble compound in which the molar ratio of the acid to methenamine is 1:4. Conductometric curves were obtained, the shapes of which are suitable for accurate and reproducible determination of the end point of titration. The results show reasonable accuracy. Good reproducibility was achieved even when small quantities of methenamine had to be determined.

Chemical Phenomena↗