Methenamine

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

Postnatal mortality was observed in the weanlings (F2 generation) of the methenamine exposed groups. Reproductive capacity and capability was not affected during this study. Thus, the dosage of 1.5-2.5 g /kg bw/day may represent a LOAEL for developmental toxicity. The doses used exceed the recommended maximum doses in respective OECD/EU guidelines.

Link to relevant study records

Reference

Endpoint:

three-generation reproductive toxicity

Remarks:

based on test type

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1970

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: old public available literature (no GLP, non guideline)

Reason / purpose for cross-reference:

reference to same study

Qualifier:

no guideline followed

Principles of method if other than guideline:

Public available literature. No guideline indicated. For details on method see IUCLID5 materials and methods section.

GLP compliance:

not specified

Limit test:

no

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

- 3-4 rats per cage
- diet and water ad libitum

Route of administration:

oral: drinking water

Vehicle:

water

Details on exposure:

Rats were given 1% methenamine in drinking water for three successive generations, up to the age of 40 weeks in the F1 and F2 groups and of 20 weeks for the F3 group, thereafter all groups were kept under observation up to week 130 of their lifetime.
An additional test group of 5 females was run on 2% methenamine from mating through lactation.

Details on mating procedure:

F0: 1 male was mated with 2 females (no further details given).
F1: 3 males were mated with 7 females
F2: 4 males were mated with 11 females

Analytical verification of doses or concentrations:

not specified

Details on analytical verification of doses or concentrations:

no details on analytical verification of doses.

Duration of treatment / exposure:

F0: 4 weeks before mating, 25-30 days of pregnancy (no further details given on F0 generation)
F1: total treatment 40 weeks, mating in week 26
F2: total treatment 40 weeks, mating in week 15
F3: total treatment 20 weeks

Frequency of treatment:

continuous via the drinking water.

Details on study schedule:

Rats were given 1% methenamine in drinking water for three successive generations, up to the age of 40 weeks in the F1 and F2 groups and of 20 weeks for the F3 group, thereafter all groups were kept under observation up to week 130 of their lifetime. The parental generation (F0) group consisted of one male and two females that were given 1% methenamine in drinking water during four weeks before mating. The treatment of the females continued until two litters of ten pups each had been weaned. The descendant F1 groups consisted of 13 males and 7 females. The females were mated to 3 males of their group. One dam died during delivery while the remaining 6 dams gave birth to a total of 36 pups from which 10 died during lactation. The resulting F2 group consisted of 15 males and of 11 females. These females were mated to 4 males of their group and delivered a total of 99 pups from which only 12 males and 12 females were further raised to yield the F3 group.
An additional test group of 5 females was run on 2% methenamine from mating through lactation. They delivered a total of 49 pups from which 16 animals per sex were continued on 2% methenamine for 50 weeks. All groups were kept under observation for over two years of age.

Remarks:

Doses / Concentrations:
0, 1 % (daily intake of approximately 1.5-2 g/kg bw/d for males and of 2-2.5 g/kg bw/d for females)
Basis:
nominal in water
3 generation study

Remarks:

Doses / Concentrations:
0, 2 % (daily intake of approximately 3.0-4.0 g/kg bw/d for males and of 4.0-5.0 g/kg bw/d for females)
Basis:
nominal in water
additional one generation study

No. of animals per sex per dose:

F0: 2 females and 1 males
F1: 7 females, 13 males
F2: 11 females, 15 males
F3: 99 pups in total, 12 of each sex were selected for treatment for an other 20 weeks

Control animals:

yes, plain diet

Details on study design:

no further details given.

Positive control:

no positive control.

Parental animals: Observations and examinations:

- water intake
no further details on F0 animals observations given.
F1, F2 and F3 animals: mortality, body weights, clinical symptoms

Oestrous cyclicity (parental animals):

not examined.

Sperm parameters (parental animals):

not examined.

Litter observations:

- number and sex of litters
- body weigh and body weight gain

Postmortem examinations (parental animals):

not details given.

Postmortem examinations (offspring):

- pathology (macroscopic and microscopic) of organs (carcinogenicity)

Statistics:

Student's t-test

Reproductive indices:

not calculated/examined.

Offspring viability indices:

not calculated/examined.

Clinical signs:

no effects observed

Body weight and weight changes:

not specified

Food consumption and compound intake (if feeding study):

not specified

Organ weight findings including organ / body weight ratios:

not examined

Histopathological findings: non-neoplastic:

not examined

Other effects:

no effects observed

Reproductive function: oestrous cycle:

not examined

Reproductive function: sperm measures:

not examined

Reproductive performance:

no effects observed

Only very limited data for parental animals were available.

Key result

Dose descriptor:

NOAEL

Effect level:

>= 1 500 - <= 2 500 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: no adverse effects on parental animals were reported.

Key result

Critical effects observed:

no

Clinical signs:

no effects observed

Mortality / viability:

mortality observed, treatment-related

Body weight and weight changes:

no effects observed

Sexual maturation:

no effects observed

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings:

no effects observed

The survival rates of all raised offspring generations (except F2) were not affected by any treatment and the body weights did not show significant differences between control and treated groups. Postnatal mortality was observed in the weanlings (F2 generation) of the methenamine exposed groups. Reproductive capacity and capability was not obviously affected during this study.
Anymore detailed information on reproductive endpoints is not available from this study since it had been primarily directed to elucidate carcinogenicity.

Key result

Dose descriptor:

LOAEL

Generation:

F2

Effect level:

>= 1 500 - <= 2 500 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: Postnatal mortality was observed in the weanlings (F2 generation) of the methenamine exposed groups.

Reproductive effects observed:

not specified

Conclusions:

Postnatal mortality was observed in the weanlings (F2 generation) of the methenamine exposed groups. Reproductive capacity and capability was not affected during this study. Thus, the dosage of 1.5-2.5 g /kg bw/day may represent a LOAEL for developmental toxicity. The doses used exceed the recommended maximum doses in respective OECD/EU guidelines.

Executive summary:

In a further study on transplacental toxicity and carcinogenesis with Wistar rats, the outcome of the exposure of animals to methenamine via drinking water was followed up in two independent experiments for one and for three successive generations. The results of the first experiment are presented in a separate endpoint study record.

In a second experiment rats were given 1% methenamine in drinking water for three successive generations, up to the age of 40 weeks in the F1 and F2 groups and of 20 weeks for the F3 group, thereafter all groups were kept under observation up to week 130 of their lifetime. The parental generation (F0) group consisted of one male and two females that were given 1% methenamine in drinking water during four weeks before mating. The treatment of the females continued until two litters of ten pups each had been weaned. The descendant F1 groups consisted of 13 males and 7 females. The females were mated to 3 males of their group. One dam died during delivery while the remaining 6 dams gave birth to a total of 36 pups from which 10 died during lactation. The resulting F2 group consisted of 15 males and of 11 females. These females were mated to 4 males of their group and delivered a total of 99 pups from which only 12 males and 12 females were further raised to yield the F3 group. An additional test group of 5 females was run on 2% methenamine from mating through lactation. They delivered a total of 49 pups from which 16 animals per sex were continued on 2% methenamine for 50 weeks. All groups were kept under observation for over two years of age. The survival rates of all raised offspring generations (except F2 generation) were not affected by any treatment and the body weights did not show significant differences between control and treated groups. Anymore detailed information on reproductive endpoints is not available from this study since it had been primarily directed to elucidate carcinogenicity. The doses used exceed the recommended maximum doses in respective OECD/EU guidelines.

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

1 500 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Quality of whole database:

Old public available literature (no GLP, non guideline)

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

Animal data:

Guideline-conform generation studies, respectively fertility studies on methenamine are not available. However, from two older studies of limited value some information can be obtained for hazard assessment with respect to reproduction.

An investigation on reproduction, was incorporated into a lifetime feeding study on Wistar rats which had received a standard diet containing 0.16% methenamine (Natvig et al., 1971). The exposed group consumed about 100 mg/kg/day of methenamine. After three months of exposure, the 16 males and 16 females of the experimental group were inbred. From the resulting F1 generation another 16 males and 16 females were fed from weaning on to the same diet as their parents. Only a few parameters were evaluated and only scarce data were given as results: the report states, that in comparison to the controls no differences for average litter size were found, and that for the F1 generation no significant differences were found for mean body weights recorded at 7, 15, and 18 weeks of age and for relative organ weights (liver, kidney, adrenals, gonads) evaluated after termination at 18 weeks of age.

In a further study on transplacental toxicity and carcinogenesis with Wistar rats (Della Porta et al., 1970), the outcome of the exposure of animals to methenamine via drinking water was followed up in two independent experiments for one and for three successive generations.

In the first experiment 12 females and 6 males were given 1% methenamine in drinking water (resulting in high daily intakes of approximately 1.5-2 g/kg bw/d for males and of 2-2.5 g/kg bw/d for females) during two weeks before mating. For the females the treatment continued during pregnancy and lactation. A similar untreated group of 12 females and 6 males served as controls. Within 25-30 days after mating 11 treated females and 11 controls became pregnant and delivered 110, respectively 118 pups. After delivery the pups of the treated and the control group were culled to 8 offspring per litter (treated group 47 m/38 f, control group 37 m/46 f). After weaning these offspring on p.n. day 32, 24 of each sex were continued on 1% methenamine in drinking water up to the 20th week of age. In treated males up to postnatal week 9 and in treated females up to postnatal week 20, the body weights were significantly lower than those of controls. However, at the beginning of the post weaning weight determination period, the initial body weights of the offspring of treated dams were already lower than those of the offspring of the controls, indicating that growth deficits were already evident. After a post treatment observation period of two weeks no differences were observed between treated and control groups in respect to organ weight and gross or microscopic alterations.

In a second experiment rats were given 1% methenamine in drinking water for three successive generations, up to the age of 40 weeks in the F1 and F2 groups and of 20 weeks for the F3 group, thereafter all groups were kept under observation up to week 130 of their lifetime. The parental generation (F0) group consisted of one male and two females that were given 1% methenamine in drinking water during four weeks before mating. The treatment of the females continued until two litters of ten pups each had been weaned. The descendant F1 groups consisted of 13 males and 7 females. The females were mated to 3 males of their group. One dam died during delivery while the remaining 6 dams gave birth to a total of 36 pups from which 10 died during lactation. The resulting F2 group consisted of 15 males and of 11 females. These females were mated to 4 males of their group and delivered a total of 99 pups from which only 12 males and 12 females were further raised to yield the F3 group. An additional test group of 5 females was run on 2% methenamine from mating through lactation. They delivered a total of 49 pups from which 16 animals per sex were continued on 2% methenamine for 50 weeks. All groups were kept under observation for over two years of age. The survival rates of all raised offspring generations were not affected by any treatment and the body weights did not show significant differences between control and treated groups. Anymore detailed information on reproductive endpoints is not available from this study since it had been primarily directed to elucidate carcinogenicity.

Human data:

During a clinical study on the pharmacokinetics of methenamine orally applied as methenamine hippurate tablets at a single dose of 1 g to healthy volunteers, methenamine had also been investigated for transplacental transfer in pregnant women during labour and for lactational transfer in nursing mothers (Allgen et al., 1979). Methenamine was found to pass the placental barrier. The concentrations in umbilical cord plasma compared to that in maternal plasma was initially low but reached the levels in maternal plasma after about 4 hours. In amniotic fluid methenamine concentrations were low and varying with no correlation to either the maternal or the umbilical cord plasma levels. When breast milk was analysed five hours after dosing, the methenamine concentrations were of the same magnitude as in maternal plasma. The amount of methenamine uptake by the child during a respective meal was calculated to be far below the usual therapeutic doses (of 5-10 mg/kg body weight) given to adults.

In an Australian clinic, a systematic trial over a 2-year period was made on 206 pregnant women who suffered from asymptomatic bacteriuria (Furness et al., 1974). One special aim was to study the effects of a disease and its special medication with methenamine salts on a number of parameters of pregnancy. The 206 patients were allocated to three treatment groups: (i) 67 patients with no treatment, (ii) 70 patients with 2 g methenamine hippurate/day, (iii) 69 patients with 4 g methenamine mandelate/day (27 mg/kg bw/day). Mean birth weights and gestation lengths showed no significant difference from the control group. The number of abortions, intrauterine deaths and fetal abnormalities in the treated groups did not differ from those of the general population. According to the authors, the statistics of the findings do not support an increase neither in prematurity nor in the incidences of fetal abnormalities or morbidity and a reduction in birth weight.

In a surveillance study conducted between 1985 and 1992 of Michigan Medicaid recipients involving 229101 completed pregnancies, 209 newborns had been exposed to methenamine during the first trimester. Eight (3.8%) major birth defects were observed. Nine major birth defects were expected due to statistical natural rate of birth defects (Briggs et al., 1994).

No congenital abnormalities were observed in the children of 3 women who had taken hexamethylenetetramine as well as 5 other drugs (choleinic sodium, phenolphthalen, papaverine HCL, methylhomatropine, and menthol) during the first two weeks of pregnancy (Siffel & Czeisel, 1995).

Effects on developmental toxicity

Description of key information

Some treatment associated developmentally toxic effects were shown for experimental animals at very high systemically toxic doses. However, no such effects were observed for the human situation. For both, in rats (at high dosages) as in beagle dogs effects were observed during the postnatal period of development in terms of pre weaning mortality and postnatal growth retardation. For the experimental data, from the study ofNatviget al., 1971, the dosage of 100 mg/kgbw/day can be considered the NOAEL/developmental toxicity for rats and from the study ofHurniandOhder, 1973, the dosage of 15 mg/kgbw/day can be considered the NOAEL/developmental toxicity for dogs. As indicated above, the experimental studies were of limited scope and of questionable validity. Human data on potentially adverse effects to development can be derived from investigations with women (clinical trials) that had been treated during pregnancy. In these studies no substance related abnormalities during the course of pregnancy or to the development of the children had been revealed, when mothers had been treated with therapeutic doses of 2 gmethenaminehippurateper day (~ 0.9 gmethenamine) or 4 gmethenaminemandelateper day (~1.9 gmethenamine) (corresponding to about 13 to 27 mgmethenamine/kgbw/day calculated on an assumed body weight of 70 kg/ person) during the period of pregnancy. Given the limited value of the animal data the quantitative risk assessment for potential effects to development will be based on the data resulting from experience in humans (NOAEL 27 mg/kg/day), as done in the EU RAR.

Link to relevant study records

Reference

Reference 1

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1987

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: public available literature (non GLP, non guideline)

Qualifier:

no guideline available

Principles of method if other than guideline:

Public available literature. No guideline indicated. For details on method see IUCLID5 materials and methods section.

GLP compliance:

not specified

Limit test:

yes

Species:

rat

Strain:

other: Alpk:AP (Wistar -derived)

Details on test animals or test system and environmental conditions:

Housing was under SPF conditions, the dams being singly housed in mesh cages with potable water and food available ad libitum. From day 18 of gestation, the cages were fitted with solid bottoms, and the dams were provided with nesting material.

Route of administration:

oral: gavage

Vehicle:

not specified

Details on exposure:

Administration by gavage, the volume being adjusted to administer 10 mL/kg bodyweight on the daily bodyweight.

Analytical verification of doses or concentrations:

not specified

Details on analytical verification of doses or concentrations:

no data on analytical verification of doses

Details on mating procedure:

Day 1 of gestation was defined as the day on which a sperm-positive vaginal smear was observed.

Duration of treatment / exposure:

Dosing was done over the period days 7-17 inclusive gestation.

Frequency of treatment:

daily

Duration of test:

Dams: 22 days (gestation)
Litters: 5 days

No. of animals per sex per dose:

9 female rats

Control animals:

yes, concurrent vehicle

Details on study design:

During validation of a Screening Assay (Chernoff-Kavlock Assay) modified for studies on rats methenamine was investigated with a group of 9 female rats treated orally (gavage) during gestation day 7 to 17 with daily doses of 1000 mg/kg bw.

Maternal examinations:

- vaginal smear
- observation of body weight on day 1, 7-17 and 22
- Number of pregnant rats
- mortality

Ovaries and uterine content:

not examined.

Fetal examinations:

- mean litter size
- total and mean number of live pups on day 1 and 5
- percentage survival
- Mean pup weight on day 1 and 5
- Mean weight gain per litter (days 1-5)

Statistics:

standard deviation
Criteria for Assessment of results:
A set of three rules was drawn up on an empirical basis to assess the results. The rules are based on both the results of the validation phase and the background data on reproductive parameters for the strain. The rules are:
1) no effect on litter size, survival, or postnatal weight gain - negative
2) reduced litter size at birth (mean less than 8) or reduced postnatal survival (less than 80%)- potential teratogen
3) reduced postnatal weight gain (less than 30%) with no reduction in survival - potential foetotoxin

Indices:

not calculated.

Historical control data:

No data available (validation of study).

Details on maternal toxic effects:

Maternal toxic effects:no effects

Details on maternal toxic effects:
In comparison to the concurrent control group a reduced weight gain was observed in treated maternal animals, indicating some toxicity or at least adverse effects of the treatment.

Key result

Dose descriptor:

NOAEL

Basis for effect level:

mortality

Remarks on result:

other: no data

Key result

Abnormalities:

no effects observed

Details on embryotoxic / teratogenic effects:

Details on embryotoxic / teratogenic effects:
Compared with the controls, the 5 pregnant dams of the treated group showed no difference in mean litter size, survival of pups and pup postnatal weight gain. However, the number of dams for which offspring could be evaluated is poor, and it is not discussed and no information is given in this study to explain, why only 5 out of 9 sperm-positive dams produced litters in the test group.

Key result

Dose descriptor:

NOAEL

Effect level:

1 000 mg/kg bw/day (nominal)

Basis for effect level:

other: teratogenicity

Key result

Dose descriptor:

NOAEL

Effect level:

1 000 mg/kg bw/day (nominal)

Basis for effect level:

other: fetotoxicity

Key result

Abnormalities:

no effects observed

Key result

Developmental effects observed:

no

Conclusions:

In a Chernoff-Kavlock assay in rats methenamine was shown to be not teratogenic and not fetotoxic at a limit concentration of 1000 mg/kg bw/day, revealed some indication for systemic toxicity under the given test conditions in the dams.

Executive summary:

During validation of a Screening Assay (Chernoff-Kavlock Assay) modified for studies on rats methenamine was investigated with a group of 9 female rats treated orally (gavage) during g.d. 7 to 17 with daily doses of 1000 mg/kg bw.

In comparison to the concurrent control group a reduced weight gain was observed in treated dams.

Compared with the controls, the 5 pregnant dams of the treated group showed no difference in mean litter size, survival of pups and pup postnatal weight gain. However, the number of dams for which offspring could be evaluated is poor, and it is not discussed and no information is given in this study to explain, why only 5 out of 9 sperm-positive dams produced litters.

Reference 2

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1973

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: old public available literature (non GLP, non guideline); low number of animals; no standard test species for this type of investigations

Qualifier:

no guideline followed

Principles of method if other than guideline:

Public available literature. No guideline indicated. For details on method see IUCLID5 materials and methods section.

GLP compliance:

not specified

Limit test:

no

Species:

other: dog

Strain:

other: Beagle

Details on test animals or test system and environmental conditions:

The 51 bitches used were from Laboratory of Bio-medical Research, Tierfarm Sisseln, Switzerland and had already successfully raised one or more litters. When 9 week old, all animals had had a combined vaccination against distemper, hepatitis and leptospiroses, and a booster vaccination was given yearly. A dose of piperazine citrate was administered at 4 and 6 week of age as well 4 and 6 weeks after each mating. Breeding bitches were housed in groups of four or five in indoor cubicles connected to an outdoor run, each pregnant bitch being transferred to an air conditioned whelping room 1 week before term.
The dogs were fed exclusively on dog pellets and were fasted each Saturday. The daily ration for bitches was 300 g, which was reduced to 200 g 1 week before term. No food was offered on the day of parturition. The animals were given 300 g on the following day, and 300 g twice daily for the next 3 weeks. From week 4 to the end of week 12, the mother was allowed 250 g twice daily, while the pups in temporary isolation received two feeds of 150 g daily. Pups of inadequately lactating mothers were supported with reconstituted cows' milk.

Route of administration:

oral: feed

Vehicle:

other: diet

Details on exposure:

Commercial grade test material was used. The test material was given at levels of 600 and 1250 ppm. Solutions containing the required daily dosage in 2.0 mL were prepared weekly and sprayed on the pellets prior to feeding. The pellets were promptly consumed.

Analytical verification of doses or concentrations:

not specified

Details on analytical verification of doses or concentrations:

no details on analytical verification of doses.

Details on mating procedure:

no details given.

Duration of treatment / exposure:

Commercial grade methenamine of unknown source and unknown purity was given at dietary levels of 600 or 1250 ppm (equivalent to doses of 15 or 31 mg/kg bw/day) at days 4 to 56 after mating.
Further groups were treated with two different dosages of formaldehyde (125 and 375 ppm), since toxicological effects of methenamine were considered to be due to the liberation of formaldehyde (FA).

Frequency of treatment:

daily

Duration of test:

56 days

No. of animals per sex per dose:

control: 11 females
low dose group: 9 females
high dose group: 10 females

Control animals:

yes, plain diet

Details on study design:

Effects of methenamine were investigated in a study with beagle dogs. Commercial grade methenamine of unknown source and unknown purity was given at dietary levels of 600 or 1250 ppm (equivalent to doses of 15 or 31 mg/kg bw/day) at days 4 to 56 after mating.

Maternal examinations:

The bitches were weighed at weekly intervals throughout pregnancy and lactation.

Ovaries and uterine content:

not examined.

Fetal examinations:

The pups were weighed at birth and twice weekly thereafter. They were inspected for visible defects immediately after birth and after 8 wk. Stillborn pups and those lost before weaning were autopsied and examined for internal and skeletal abnormalities.

Statistics:

not indicated.

Indices:

no indices were calculated.

Historical control data:

no historical data given.

Details on maternal toxic effects:

Maternal toxic effects:no effects

Details on maternal toxic effects:
From the 11 mated control bitches 9 turned out to be pregnant and provided litters. From the 9 bitches mated in the 15 mg/kg dose group 8 turned out to be pregnant and provided litters. From the 10 bitches mated in the 30 mg/kg dose group 9 turned out to be pregnant. One pregnant bitch in this group was severely injured in a fight and had to be eliminated. Thus only 8 litters were derived from this group. Further groups were treated with two different dosages of formaldehyde (125 and 375 ppm), since the toxicological effects of methenamine were considered to be due to the liberation of formaldehyde (FA).
Treatment at either dose level did not affect pregnancy rates, mean length of gestation, mean litter size or body weight gain of the mothers. Body weight of the bitches increased regularly during pregnancy in all groups and the duration of gestation was unaffected by the treatment.

Key result

Dose descriptor:

NOAEL

Effect level:

15 mg/kg bw/day (nominal)

Basis for effect level:

other: developmental toxicity

Key result

Dose descriptor:

LOAEL

Effect level:

31 mg/kg bw/day (nominal)

Basis for effect level:

other: developmental toxicity

Key result

Abnormalities:

no effects observed

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:yes

Details on embryotoxic / teratogenic effects:
The mean litter size was within the normal range for all groups (controls, FA 125 ppm, FA 375 ppm, methenamine 600 ppm, methenamine 1250 ppm: 6.7, 5.4, 7.1, 6.3, 7.0). In the group that had received the higher dose of methenamine, the percentage of stillborn pups was higher than in the other groups, due to the fact that in one litter of nine pups only two were born alive, which indicates a potential problem with the respective bitch. No skeletal or any other malformation were observed in any of the stillborn pups. During the first month there was a retardation of growth in the group given the higher dose of methenamine, coinciding with an increase in mortality (no data provided). In the same group the percentage of pups that survived to weaning was lower than in the other groups (no data provided). All dogs observed for a more prolonged period have been normal in behavior, appearance, motility and muscular co-ordination. The dogs observed up to 9 months were used for various other investigations, for which they were eventually killed and autopsied. No malformations were found. The 18 dogs transferred to the breeding colony have been under observation for nearly 2 yr. Neither these adults nor their litters have shown any signs of physiological or skeletal abnormalities or disorders of reproduction.

Key result

Dose descriptor:

other:

Remarks:

No NOAEL determined

Remarks on result:

not measured/tested

Key result

Abnormalities:

not specified

Key result

Developmental effects observed:

no

Conclusions:

In this study on beagle dogs the daily dosage of 15 mg/kg bw did not produce any significant effects on the development of the offspring, whereas at a daily dosage of 31 mg/kg bw lower pup survival and pup growth retardation were observed, compared to concurrent control. However, no historical control data are given.

Executive summary:

Effects of methenamine were also investigated in a study with beagle dogs. Commercial grade methenamine of unknown source and unknown purity was given at

dietary levels of 600 or 1250 ppm (equivalent to doses of 15 or 31 mg/kg bw/day) at days 4 to 56 after mating. From the 11 mated control bitches 9 turned out to be pregnant and provided litters. From the 9 bitches mated in the 15 mg/kg dose group 8 turned out to be pregnant and provided litters. From the 10 bitches mated in the 30 mg/kg dose group 9 turned out to be pregnant. One pregnant bitch in this group was severely injured in a fight and had to be eliminated. Thus only 8 litters were derived from this group. Further groups were treated with two different dosages of formaldehyde (125 and 375 ppm), since the toxicological effects of methenamine were considered to be due to the liberation of formaldehyde (FA). The bitches were weighed at weekly intervals throughout pregnancy and lactation. The pups were weighed at birth and twice weekly thereafter. They were inspected for visible defects immediately after birth and after 8 wk. Stillborn pups and those lost before weaning were autopsied and examined for internal and skeletal abnormalities. Treatment at either dose level did not affect pregnancy rates, mean length of gestation, mean litter size or body weight gain of the mothers. Body weight of the bitches increased regularly during pregnancy in all groups and the duration of gestation was unaffected by the treatment. The mean litter size was within the normal range for all groups (controls, FA 125 ppm, FA 375 ppm, methenamine 600 ppm, methenamine 1250 ppm: 6.7, 5.4, 7.1, 6.3, 7.0). In the group that had received the higher dose of methenamine, the percentage of stillborn pups was higher than in the other groups, due to the fact that in one litter of nine pups only two were born alive, which indicates a potential problem with the respective bitch. No skeletal or any other malformation were observed in any of the stillborn pups. During the first month there was a retardation of growth in the group given the higher dose of methenamine, coinciding with an increase in mortality (no data provided). In the same group the percentage of pups that survived to weaning was lower than in the other groups (no data provided). All dogs observed for a more prolonged period have been normal in behavior, appearance, motility and muscular co-ordination. The dogs observed up to 9 months were used for various other investigations, for which they were eventually killed and autopsied. No malformations were found. The 18 dogs transferred to the breeding colony have been under observation for nearly 2 yr. Neither these adults nor their litters have shown any signs of physiological or skeletal abnormalities or disorders of reproduction. The NOAEL/developmental toxicity of this study on dogs is 15 mg/kg bw/d.

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

27 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

Public available literature (non GLP, non guideline)

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Additional information

Only limited information is available on investigations on developmental toxicity. Guideline conform developmental toxicity studies on methenamine are not available.

During validation of a Screening Assay (Chernoff-Kavlock Assay) modified for studies on rats (Wickramaratne, 1987) methenamine was investigated with a group of 9 female rats treated orally (gavage) during g.d. 7 to 17 with daily doses of 1000 mg/kg bw. In comparison to the concurrent control group a reduced weight gain was observed in treated animals. Compared with the controls, the 5 pregnant dams of the treated group showed no difference in mean litter size, survival of pups and pup postnatal weight gain. However, the number of dams for which offspring could be evaluated is poor, and it is not discussed and no information is given in this study to explain, why only 5 out of 9 sperm-positive dams produced litters.

Effects of methenamine were also investigated in a study with beagle dogs (Hurni and Ohder, 1973). Commercial grade methenamine of unknown source and unknown purity was given at dietary levels of 600 or 1250 ppm (equivalent to doses of 15 or 31 mg/kg bw/day) at days 4 to 56 after mating. From the 11 mated control bitches 9 turned out to be pregnant and provided litters. From the 9 bitches mated in the 15 mg/kg dose group 8 turned out to be pregnant and provided litters. From the 10 bitches mated in the 30 mg/kg dose group 9 turned out to be pregnant. One pregnant bitch in this group was severely injured in a fight and had to be eliminated. Thus only 8 litters were derived from this group. Further groups were treated with two different dosages of formaldehyde (125 and 375 ppm), since the toxicological effects of methenamine were considered to be due to the liberation of formaldehyde (FA). The bitches were weighed at weekly intervals throughout pregnancy and lactation. The pups were weighed at birth and twice weekly thereafter. They were inspected for visible defects immediately after birth and after 8 wk. Stillborn pups and those lost before weaning were autopsied and examined for internal and skeletal abnormalities. Treatment at either dose level did not affect pregnancy rates, mean length of gestation, mean litter size or body weight gain of the mothers. Body weight of the bitches increased regularly during pregnancy in all groups and the duration of gestation was unaffected by the treatment. The mean litter size was within the normal range for all groups (controls, FA 125 ppm, FA 375 ppm, methenamine 600 ppm, methenamine 1250 ppm: 6.7, 5.4, 7.1, 6.3, 7.0). In the group that had received the higher dose of methenamine, the percentage of stillborn pups was higher than in the other groups, due to the fact that in one litter of nine pups only two were born alive. No skeletal or any other malformation were observed in any of the stillborn pups. During the first month there was a retardation of growth in the group given the higher dose of methenamine, coinciding with an increase in mortality (no data provided). In the same group the percentage of pups that survived to weaning was lower than in the other groups (no data provided). All dogs observed for a more prolonged period have been normal in behavior, appearance, motility and muscular co-ordination. The dogs observed up to 9 months were used for various other investigations, for which they were eventually killed and autopsied. No malformations were found. The 18 dogs transferred to the breeding colony have been under observation for nearly 2 yr. Neither these adults nor their litters have shown any signs of physiological or skeletal abnormalities or disorders of reproduction. The NOAEL/developmental toxicity of this study on dogs is 15 mg/kg bw/d.

Data from investigations on chick embryos (Korhonen et al., 1983) where 0.25 mg methenamine/egg was applied to three-day old embryos in ovo via dropping onto the inner shell membrane did not produce any effects above the background of vehicle controls.

Toxicity to reproduction: other studies

Additional information

Studies on methenamine according to current guidelines are not available for reproductive or developmental toxicty. Presently available data come from a developmental screening assay and from 3 older single dose mammalian studies in rats and one two dose study with dogs.

During the dietary study with rats (Natvig et al., 1971) the daily dosage of about 100 mg methenamine/kg bw did not reveal any significant effects on the investigated parameters. During the rat study with drinking water administration (Della Porta et al., 1970) the dosage of 1.5-2.5 g /kg bw/day did reveal effects: during the first experiment growth retardation in terms of significantly lower body weights was determined in the pups after weaning. Birth weights and postnatal body weight development of the weanlings had not been determined. Yet, at the beginning of the post weaning weight determinations the initial body weights of the offspring of treated dams was already lower than in the offspring of the controls, indicating that growth deficits were already endowed with. In the second experiment postnatal mortality was observed in the weanlings (F2 generation) of the methenamine exposed groups. Reproductive capacity and capability was not affected during this study. Thus, the dosage of 1.5-2.5 g /kg bw/day, which already exeeds the recommended limit dose for such a type of study, may represent a LOAEL for developmental toxicity. During the Chernoff-Kavlock Assay with rats (Wickramaratne, 1987) the dosage of 1 g/kg bw/day (gavage) did not reveal indications for any effects upon pup viability and postnatal pup body weights. However, the number of dams for which offspring could be evaluated is poor, and it is not discussed and no information is given in this study to explain, why only 5 out of 9 sperm-positive dams produced litters. In the study on beagle dogs (Hurni and Ohder, 1973) the daily dosage of 15 mg/kg bw did not produce any significant effects on the development of the offspring, whereas at a daily dosage of 31 mg/kg bw lower pup survival and pup growth retardation were observed.

Taken for its own, neither of these studies sufficiently meets requirements for a sound hazard evaluation with respect to toxicity to reproduction due to poor documentation, use of small animal numbers only, insufficient investigation of reproductive and developmental parameters, and any teratogenic properties not adequately studied. Therefore, the evaluation of the available experimental data can only be based on a synoptic view of all studies.

Taking into consideration that in the rat studies high dose levels (> 1000 mg methenamine/kg body weight/day) had been under investigation, the overall information of these studies may indicate that an overt toxic potential of methenamine adverse to reproductive performance and capability is rather unlikely to be suspected. Methenamine did not reveal a marked potential to adversely affect fertility in rats. Even at longer periods of administration with high doses reproductive capacity and/or capability did not differ from that of the untreated controls. Thus, the dosage of 1.5-2.5 g/kg bw/day can be considered the NOAEL/fertility from experimental data. Treatment associated developmentally toxic effects were shown for experimental animals, however, no such effects were observed for the human situation. For both, in rats (at high dosages) as in beagle dogs effects were observed during the postnatal period of development in terms of pre weaning mortality and postnatal growth retardation. For the experimental data, from the study of Natvig et al., 1971, the dosage of 100 mg/kg bw/day can be considered the NOAEL/developmental toxicity for rats and from the study of Hurni and Ohder, 1973, the dosage of 15 mg/kg bw/day can be considered the NOAEL/developmental toxicity for dogs. As indicated above, the experimental studies were of limited scope and of questionable validity. Human data on potentially adverse effects to development can be derived from investigations on women that had been treated during pregnancy. In these studies no substance related abnormalities during the course of pregnancy or to the development of the children had been revealed, when mothers had been treated with therapeutic doses of 2 g methenamine hippurate per day (~ 0.9 g methenamine) or 4 g methenamine mandelate per day (~1.9 g methenamine) (corresponding to about 13 to 27 mg methenamine/kg bw/day calculated on an assumed body weight of 70 kg/ person) during the period of pregnancy. Given the limited value of the animal data it is proposed to base quantitative risk assessment for effects adverse to development on the data resulting from experience in humans (NOAEL 27 mg/kg/day).

Justification for classification or non-classification

Classification, Labelling, and Packaging Regulation (EC) No 1272/2008

The available experimental test data are reliable and suitable for classification purposes under Regulation (EC) No 1272/2008. As a result the substance is not considered to be classified under Regulation (EC) No 1272/2008.