1H-1,2,4-Triazole-1-carboxamide, 4-amino-N-(1,1-dimethylethyl)-4,5-dihydro-3-(1-methylethyl)-5-oxo-

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Inital study: 29 September 1997 to 30 October 1997. Supplementary study: 23 August 1999 to 4 November 1999

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Test material administered from gestation day 6 to 19, rather than the complete gestaional period as per current guidelines

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1999

Report date:

1999

Reference 2

Reference Type:

study report

Title:

Unnamed

Year:

2000

Report date:

2000

Reference 3

Reference Type:

study report

Title:

Unnamed

Year:

1995

Report date:

1995

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Version / remarks:

(1981)

Deviations:

yes

Remarks:

under current guidance test material should be administered throughout gestation. In this study expsoure was limited to GD 6-19

Test guideline 2

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.3700 (Prenatal Developmental Toxicity Study)

Version / remarks:

(1998)

Deviations:

yes

Remarks:

under current guidance test material should be administered throughout gestation. In this study expsoure was limited to GD 6-19

Test guideline 3

Qualifier:

according to guideline

Guideline:

EU Method B.31 (Prenatal Developmental Toxicity Study)

Version / remarks:

(1995)

Deviations:

no

Test guideline 4

Qualifier:

according to guideline

Guideline:

other: Health Canada, Canada Gazette, Part II, Vol. 122, No.2 (1988)

Deviations:

no

Test guideline 5

Qualifier:

according to guideline

Guideline:

other: JMAFF 59 NohSan No. 4200 (Guidance on toxicology study data for application of agriculture chemical registration) (1985)

Deviations:

no

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

4-amino-N-tert-butyl-5-oxo-3-(propan-2-yl)-4,5-dihydro-1H-1,2,4-triazole-1-carboxamide

EC Number:

603-373-3

Cas Number:

129909-90-6

Molecular formula:

C10H19N5O2

IUPAC Name:

4-amino-N-tert-butyl-5-oxo-3-(propan-2-yl)-4,5-dihydro-1H-1,2,4-triazole-1-carboxamide

Constituent 2

Reference substance name:

MKH 3586 Technical

IUPAC Name:

MKH 3586 Technical

Details on test material:

- Name of test material (as cited in study report): MKH 3586 Technical
- Substance type: Powder
- Analytical purity: 98.1 - 98.5% (initial study) 97.8 - 97.9% (supplementary study)
- Lot/batch No.: 05362/0005
- Expiration date of the lot/batch: confirmed stable for the duration of the study

Test animals

Species:

rat

Strain:

Sprague-Dawley

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

CMC (carboxymethyl cellulose)

Remarks:

0

Analytical verification of doses or concentrations:

yes

Details on mating procedure:

2 females were housed with one male until vaginal smear confirmed presence of sperm.

Duration of treatment / exposure:

GD 6-19 / oral exposure

Frequency of treatment:

once/day

Duration of test:

14 days

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
Initial study: 0, 15, 100, 300 mg/kg/day
Basis:
analytical conc.

Doses / concentrations 2

Remarks:

Doses / Concentrations:
Supplementary study: 0, 5, 15 mg/kg/day
Basis:
analytical conc.

No. of animals per sex per dose:

30 females/group

Control animals:

yes, concurrent vehicle

Results and discussion

Results: maternal animals

Effect levels (maternal animals)

1

Dose descriptor:

NOAEL

Effect level:

ca. 15 mg/kg bw/day (actual dose received)

Based on:

other: decreased bodyweight, food consumption and increased absolute liver weight

Basis for effect level:

other: maternal toxicity

2

Dose descriptor:

NOAEL

Effect level:

ca. 15 mg/kg bw/day (actual dose received)

Based on:

other: multiple skeletal development retardations (incomplete ossification/unossification)

Basis for effect level:

other: developmental toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:yes. Remark: incompletely ossified bones

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Any other information on results incl. tables

INITIAL STUDY:

PARENTAL ANIMALS:

Clinical signs and mortality:

Clinical signs of toxicity included hard-stool observed in both the intermediate (9/20) and high dose groups (22/27), with clonic convulsions observed on two occasions in two dams in the high dose group.  The death of one pregnant female at 300 mg/kg/day was not clearly treatment related.

 

Bodyweight:

Significant reduction (p<0.01) was observed in the high dose group during gestation days 7-20. In addition, statistically significant decreases on body weight gain during GD 2-19 (-37%) and 0-20 (-32%) were also observed. Similar effects, but to a lesser extent were also observed in the intermediate dose group. In contrast to both the intermediate and high dose groups, the low dose group showed statistically significant (p<0.05) decreased body weight at all time points, including GD 0, 2 and 4 which were measured prior to treatment with the test material. Therefore the difference in mean body weight between the control and low dose group, which began on GD 0 was simply maintained through the study and not considered test material related.

 

Food consumption:

Statistically significant decreases, which were considered test material related were observed in the intermediate (p<0.05 / p<0.01 GD 6-9) and high (P<0.01 GD 6-12 and 14-15) dose groups.  

 

Reproductive function and performance:

There were no treatment related effects on either the fertility index or gestation index

 

Post mortemresults:

Parental animals: No gross necropsy observations suggestive of a relationship to treatment with MKH 3586.

Organ weights: absolute and relative increases (p< )in liver weights were observed in the high dose group, where as only the relative liver weight was increased in the intermediate dose group. An increase in liver weight was observed in the low dose group, however this observation was not considered test material related based on the discussion above.

Uteri data: no significant difference in pre or post implantation loss or on early or late resorptions were observed. In the control and intermediate dose groups all litters contained only viable foetuses. In the low dose group one dam had a litter with 10 viable foetuses and 1 non-viable foetus and in the high dose group one dam had a litter with 12 viable foetuses with 1 non viable foetus with another dam had a litter with 2 non-viable foetuses only.

 

Foetuses: no significant differences in litter size, number and proportion of live foetuses/litter or the median % of male foetuses were observed. A significant (p<0.01) decrease in the male, female and combined mean foetal weights were observed in the high dose group. No effect on foetal weight was observed in either the low or intermediate dose group.

External malformations/variations: no significant effects on either foetal or litter incidence of external malformation were observed in any doe group

Visceral malformations/variations: no significant foetal visceral malformation were noted in any dose group. Foetal visceral variations were observed independent of dose.

Skeletal malformations/variations: no significant test material foetal skeletal malformations were observed. Foetal skeletal variations were observed in all litters, in virtually all foetuses. Statistically significant increased variations were observed to the greatest extent in the high dose group and to a lesser extent in the intermediate group. Whilst variations in the low dose group were also increased above the concurrent control, these increases were within the historical control and failed to show evidence of a dose response. e.g. 62.9% of unossified caudal arches were observed in foetuses of the low dose group, this was also noted in intermediate dose group with 63% incidence. The incidence of incompletely ossified bones was artificially increased due to the skeletal staining methodology. This increase may be quantified by comparing the mean incidence of a given finding in the concurrent control with the mean incidence rate for the same finding in the historical control. In general, the mean incidence rate for incompletely ossified bones in the concurrent control group was typically 20-30% greater than the mean in the historical control.  Based on this observation the historical control range would also be expected to increase by a similar margin. Therefore the incompletely ossified bones observed in the low dose group were just outside the historical control range would probably fall within the range if the historical control database consisted of foetuses processed in a manner similar to this study data. Based on this, the variations observed in the low dose group were not considered test material related.

 

Table 7.8.2-1:Selected post mortem results

Dose (ppm)	0	15	100	300
No/gp	30	30	30	30
Reproductive function and performance
Fert. Index (%)	83.3	93.3	66.7	90.0
Gest. Index (%)	100	100	100	96.2
Mating index (%)	100	100	100	100.
Organ weights
Liver [abs]	14.7 (25)	14.5 (28)	15.5 (20)	16.4** (26)
Liver [rel]	3.9 (25)	4.1 (28)*	4.5** (20)	5.0** (26)
Litter data
Mean weight: male (g)	3.9	3.9	3.7	3.4**
Mean weight: female (g)	3.7	3.7	3.6	3.1**
Mean weight: combined (g)	3.58	3.8	3.7	3.3**
Histology
Viable foetuses	25	28	20	25
Non-viable foetuses	0	1	0	2

 

SUPPLEMENTARY STUDY:

Clinical signs:no test material related clinical signs were observed.

Parental body weight: whilst a statistically significant decrease in bodyweight on GD 12 and 13 in the 15 mg/kg/day dose group and on GD 13 in the 5 mg/kg/day group was observed, these were within the normal range of variability and were not considered test material related.

Food consumption: statistically significant decrease in food consumption was observed during GD 8-9 in the 15 mg/kg./day group, again this was within the normal range of variability and were not considered test material related.

Maternal necropsy: no test material related changes observed.

Reproductive parameters: no test material related changes observed.

 

Embryo implantation / resorptions: no test material related changes were observed in the number of corpora lutea or the number of implantation sites. There were no effects on resorptions (early or late) or pre / post implantation loss.

Litter effects: a significant increase in the number of males/litter was observed in the 15 mg/kg group, this finding was not originally observed and is not considered test material related. No effects were observed on litter size, the number and proportion of live foetuses/litter or foetal or placental weights.

Foetal skeletal malformations/variations: the incidence of skeletal variation observed was considered to be within the normal variation expected.

Applicant's summary and conclusion

Conclusions:

Based on the result of this study, along with the supplementary study developmental effects were observed at both 100 and 300 mg/kg/day, and consisted primarily of incompletely ossified bones. Maternal toxicity at 100 mg/kg/day included decreased bodyweight and food consumption and increased absolute liver weight. At 300 mg/kg/day effects included increased incidence of non-viable foetuses and a statistically significant decrease in foetal weight. Both the maternal and developmental NOAEL is considered to be 15 mg/kg/day. The developmental effects occurred only at dose levels that produced maternal toxicity.

Executive summary:

MKH 3586 was administered orallyviagavage groups (30) pregnant female rats at concentrations of 0, 15, 100 and 300 mg/kg/day from gestation day 6 to 19. Dams were culled on GD 20 and foetuses were removed by caesarean section and examined. 

 

Clinical signs of toxicity included hard stool observed in 9/20 dams at 100 mg/kg/day and 22/27 dams at 300 mg/kg/day beginning several days after dosing began. At 3000 mg/kg/day clonic convulsions were observed on 2 occasions in 2/27 dams. Body weights were dose-dependently decreased (p<0.05) at 100 (-7 to -8%) and 300 (-4 to -13%) mg/kg/day on GD 7-20, resulting in decreased body weight gains for GD 6-20. Gravid uterine weights were slightly lower than controls (-14%, buit not considered statistically significant), this was due in part to lower foetal weights. Food consumption was decreased (p<0.05) at 100 and 300 mg/kg/day. The high dose group dams also demonstrated increased (p<0.05) absolute and relative liver weights.

 

There were no abortions, premature deliveries, late resorptions or complete litter resorptions. No effects of treatment were noted on numbers of litters, live foetuses, dead foetuses early resorptions, placental weight, sex ratio or post implantation losses. Decreased (p<0.01) body weights were observed in the high dose group male and female foetuses. There were no treatment-related external, visceral or skeletal variations or malformations. Multiple dose-related increases (p<0.05) in retardations of foetal skeletal development were noted. At doses of 100 and 300 mg/kg/.day incomplete ossification/unossification was observed in parietal, interparietal, supraoccipital and squamosal bones, zygoma, pubis, xiphoid and metacarpals. Additionally at 300 mg/kg/day incomplete ossification/unossification was also observed in nasal bones, lumbar, caudal and sacral arches, caudal centra, metatarsals, manubrim, sternebrae [segments 2, 3, 4 and 5] and ribs.

 

A supplemental developmental study was undertaken to evaluate the potential relationship between the test material and the foetal skeletal effects noted in this study. In this supplementary study no skeletal effects were observed, confirming that effects observed initially at 15 mg/.kg were probably not test material related.

 

Based on the result of this study, along with the supplementary study developmental effects were observed at both 100 and 300 mg/kg/day, and consisted primarily of incompletely ossified bones. Maternal toxicity at 100 mg/kg/day included decreased bodyweight and food consumption and increased absolute liver weight. At 300 mg/kg/day effects included increased incidence of non-viable foetuses and a statistically significant decrease in foetal weight. Both the maternal and developmental NOAEL is considered to be 15 mg/kg/day. The developmental effects occurred only at dose levels that produced maternal toxicity.