pymetrozine (ISO); (E)-4,5-dihydro-6-methyl-4-(3-pyridylmethyleneamino)-1,2,4-triazin-3(2H)-one

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

16 Sep 1991 to 15 Oct 1991

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1992

Report date:

1992

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Version / remarks:

Adopted May 1981

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

other: U.S. EPA FIFRA 83-3 "Teratogenicity study"

Version / remarks:

October 1982

Deviations:

no

Test guideline 3

Qualifier:

according to guideline

Guideline:

other: U.S. EPA TSCA 798.4900 "Developmental toxicity study",

Version / remarks:

August 1987

Deviations:

no

Test guideline 4

Qualifier:

according to guideline

Guideline:

other: Japanese MAFF 59 NohSan No. 4200, "Teratogenicity study"

Version / remarks:

January 1985

Deviations:

no

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

6-methyl-4-[(E)-[(pyridin-3-yl)methylidene]amino]-2,3,4,5-tetrahydro-1,2,4-triazin-3-one

EC Number:

602-927-1

Cas Number:

123312-89-0

Molecular formula:

C10H11N5O

IUPAC Name:

6-methyl-4-[(E)-[(pyridin-3-yl)methylidene]amino]-2,3,4,5-tetrahydro-1,2,4-triazin-3-one

Test material form:

solid: particulate/powder

Test animals

Species:

rabbit

Strain:

other: Thomae Russian breed, Chbb:HM

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: at least 3 months
- Weight at study initiation: 2129 to 2661 g
- Housing: The study was carried out under optimal hygienic condition (OHC). The animals were housed individually in Heinkel batteries with wire grid floor.
- Diet: ad libitum, Pelleted, certified standard diet
- Water: tap water ad libitum
- Acclimation period: at least 7 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 19 ± 2
- Humidity (%): 50 ± 20
- Air changes (per hr): approximately 16
- Photoperiod (hrs dark / hrs light): 12/12 (6 a.m. to 6 p.m.)

IN-LIFE DATES:
16 Sep 1991 to 15 Oct 1991

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

CMC (carboxymethyl cellulose)

Remarks:

0.5% (w/w) aqueous solution

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
Test substance-vehicle mixtures were prepared fresh weekly with a high-speed homogenizer. During administration the homogeneity of the mixtures was maintained by means of a magnetic stirrer.

DIET PREPARATION
- Rate of preparation of diet: weekly

VEHICLE
- Amount of vehicle (if gavage): 4 mL/kg

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Samples of approximately 2 mL volume were taken once before dosing and once after dosing. The samples from before dosing were taken from the top, middle and bottom of the container; the samples from after dosing were taken from the middle of the container.
All samples were stored at approximately -20 degrees Celsius until analysis. The samples for the stability test were allowed to stand at room temperature for the duration of the dosing period and then frozen.

Details on mating procedure:

IMPREGNATION PROCEDURE: ARTIFICIAL INSEMINATION
Nulliparous females, individually identified by an ear tag, were quarantined and acclimated to the facility environment and diet for at least seven days before being inseminated and placed on study. During this time, they were checked for general health. Only healthy animals were placed on study. Approximately 1 hour after i.v. injection of a synthetic releasing hormone (0.1 - 0.2 mL/kg Receptal (busereline acetate)), females were artificially inseminated with diluted semen (in sterile physiological saline) from bucks of the same strain.
The day of insemination was designated Day 0 of pregnancy.
Note: With insemination by natural mating, day of pregnancy is also referred to as day post coitum (p.c.) in raw data and report. In the present study using artificial insemination, the term "post coitum" or "p.c." is to be read as "post insemination".

Duration of treatment / exposure:

Day 7 through 19 p.c.

Frequency of treatment:

Daily

Duration of test:

13 days

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

10 mg/kg bw/day (actual dose received)

Remarks:

Group 2, low dose.

Doses / concentrations 2

Dose / conc.:

75 mg/kg bw/day (actual dose received)

Remarks:

Group 3, mid dose.

Doses / concentrations 3

Dose / conc.:

125 mg/kg bw/day (actual dose received)

Remarks:

Group 4, high dose.

No. of animals per sex per dose:

20

Control animals:

yes

Details on study design:

- Dose selection rationale: The dose levels were selected based on a previous range-finding study.

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily, including mortality

DETAILED CLINICAL OBSERVATIONS: No

BODY WEIGHT: Yes
- Time schedule for examinations: daily

FOOD CONSUMPTION AND COMPOUND INTAKE: Yes
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/day: Yes
- Time schedule for examinations: days 4, 7, 12, 16, 20, 24 and 29 p.c.

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 29
- Organs examined: Macroscopic pathological examination of the main organs of the thoracic and abdominal cavities, in particular the genitals.

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes
Examinations included:
- Gravid uterus weight: Yes (including contents)
- Number of corpora lutea: Yes (in each ovary)
- Number of implantations: Yes (life and dead)
- Number of early resorptions: Yes
- Number of late resorptions: Yes
- Other: abortion sites

Fetal examinations:

- External examinations: Yes: all per litter (All body regions (e.g. generalized or localized edema, hemorrhage), extremities (e.g. absent, shortened, deformed, additional), tail (e.g. absent, shortened, kinked), trunk (e.g. failure of closure of spinal cord, atresia of a body orifice, omphalocele), head (e.g. absent, reduced, deformed), brain (e.g. cranioschisis, encephalocele, exencephaly), eyes (e.g. absent, reduced, open), pinnae (e.g. absent), jaws (e.g. absent, shortened), oral orifice (e.g. absent), cleft lip/cleft palate).
- Soft tissue examinations: Yes: all per litter (skin, skull elements, central nervous system, eyes, body cavities, respiratory system, digestive system, endocrine system, circulatory system, excretory system, genital system).
- Skeletal examinations: Yes: half litter (cranial skeleton, axial skeleton, appendicular skeleton). Additionally half litter is subjected to examination of the skull for wide fontanels of the fronto-parietal region of the skull.

Statistics:

Statistical analysis of continuous data (e.g. body weight, feed consumption) was performed using the Analysis of Variance Procedure (ANOVA) followed by Dunnett's t-Test in case of a significant result in the ANOVA.
Categorical data (e.g. malformation counts) were analysed using Chi-Square test followed by Fisher's Exact test in case of a significant result in the Chi-Square test.
Non-parametric data (e.g. mean percent affected foetuses/litter) were analysed using the Kruskal-Wallis nonparametric analysis of variance test followed by Mann-Whitney u-test.

Results and discussion

Results: maternal animals

General toxicity (maternal animals)

Clinical signs:

effects observed, non-treatment-related

Description (incidence and severity):

One dam in the 75 mg/kg group had hair loss from day 26. This was not considered to be treatment-related.

Dermal irritation (if dermal study):

not examined

Mortality:

mortality observed, treatment-related

Description (incidence):

Three animals died prematurely: one dam in the control group on day 16, and two in the 125 mg/kg group on days 16 and 17 respectively. One of these had haemorrhagic perineal discharge on the previous day 15.
Another dam in the 125 mg/kg group was electively sacrificed after abortion on day 19.
Although there were no necropsy findings to differentiate the death of the control dam and the two in the 125 mg/kg group, the two deaths and the abortion in the 125 mg/kg group were presumed to be treatment-related.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Mean body weights were dose-relatedly reduced in the 75 and 125 mg/kg groups, compared to controls, significantly in the 125 mg/kg group from day 18 on.
At 75 mg/kg bw/d, mean maternal body weight gain was reduced from days 7 to 19, achieving 38% of the control value. At 125 mg/kg bw/d, there was even a loss of mean body weight, particularly from days 16 to 20. A statistically significant difference of mean body weights from control was achieved from day 18.
Body weights and body weight gain were unaffected by treatment in the 10 mg/kg group.
Mean body weight and body weight gain values can be found in table 1 in 'Any other information on results incl. tables'.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Feed consumption was significantly and dose-dependently reduced in the 75 and 125 mg/kg groups during the treatment period (days 7 to 19 of pregnancy).
Feed consumption in the 10 mg/kg group was not affected.

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

effects observed, non-treatment-related

Description (incidence and severity):

In the control group, the dam which was found death had haemorrhagic contents of the abdominal cavity and gall bladder dilatation.
In the 10 mg/kg group, one dam had fluid stomach contents and gall bladder dilatation. Another dam had a constriction in the middle of both uterine horns (and was not pregnant).
In the 75 mg/kg group, one dam had a dilated gall bladder.
In the 125 mg/kg group, the dam killed after aborting on day 19 and the dam which was found dead on day 16 had gas in stomach and gall bladder dilatation. Another dam, found dead on day 17 had mottled dark red lungs.
All the above findings, with the exception of abortion, are commonly observed at necropsy, and the findings in the high dose animals can therefore not be attributed with any certainty to the treatment.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

not examined

Histopathological findings: neoplastic:

not examined

Other effects:

effects observed, non-treatment-related

Description (incidence and severity):

Mean carcass weights were slightly lower than controls in the 75 and 125 mg/kg groups, and net weight loss slightly higher, but these effects were not statistically significant.

Maternal developmental toxicity

Number of abortions:

effects observed, treatment-related

Description (incidence and severity):

One dam in the 125 mg/kg group had an abortion on day 19.

Pre- and post-implantation loss:

effects observed, treatment-related

Description (incidence and severity):

Preimplantation losses did not differ between groups.
Post-implantation losses as a whole were dose-relatedly increased in the 75 and 125 mg/kg groups.

Total litter losses by resorption:

effects observed, treatment-related

Description (incidence and severity):

One dam in the 75 mg/kg group, and three in the 125 mg/kg group had total resorptions.

Early or late resorptions:

effects observed, treatment-related

Description (incidence and severity):

Early resorptions (mean percent per animal) were dose-relatedly increased in the 75 and 125 mg/kg groups.
Late resorptions were not significantly increased in any treatment group or the control group.

Dead fetuses:

no effects observed

Changes in pregnancy duration:

no effects observed

Description (incidence and severity):

There were no early deliveries.

Changes in number of pregnant:

effects observed, non-treatment-related

Description (incidence and severity):

The number of pregnant animals per group were: 17/20, 17/20, 18/20 and 19/20 for the control to high dose group, respectively.
The number of dams per group with viable fetuses at scheduled necropsy was 16, 17, 17, and 13 for control to high dose group, respectively.

Other effects:

no effects observed

Description (incidence and severity):

Gravid uterus weights were not significantly affected by treatment.

Details on maternal toxic effects:

An overview of the number of pregnant dams and dams with; live foetuses, total resorption, early delivery or abortion can be found in table 2 in 'any other information on results incl tables.

Effect levels (maternal animals)

Key result

Dose descriptor:

NOAEL

Effect level:

10 mg/kg bw/day (actual dose received)

Based on:

test mat.

Basis for effect level:

body weight and weight gain

food consumption and compound intake

Maternal abnormalities

Abnormalities:

no effects observed

Results (fetuses)

Fetal body weight changes:

no effects observed

Description (incidence and severity):

Fetal body weights were not significantly affected by treatment.

Reduction in number of live offspring:

effects observed, treatment-related

Description (incidence and severity):

The number of live offspring was reduced in the 125 mg/kg group. The number of live offspring was; 103, 116, 110 and 72 for the control to high dose group, respectively.
It should be noted that in none of the dams dead foetuses were found.

Changes in sex ratio:

no effects observed

Changes in litter size and weights:

effects observed, treatment-related

Description (incidence and severity):

Fetal body weight was not significantly affected by the treatment.
Mean litter size was lower in the 125 mg/kg group than in controls.

Changes in postnatal survival:

not examined

External malformations:

effects observed, non-treatment-related

Description (incidence and severity):

One foetus in the 10 mg/kg group had a domed head (and was found to have hydrocephalus at visceral examination). This finding has been observed in historical controls, and is not considered treatment-related.
An overview of the external malformations can be found in table 4 in 'Any other information on results incl. tables'.

Skeletal malformations:

effects observed, treatment-related

Description (incidence and severity):

According to the authors there were no skeletal malformations in this study. However, reduced pubis was observed in the 75 and 125 mg/kg groups and reported as anomaly. This finding is considered to be a malformation according to the website “www.devtox.org”, as reported in the 'Renewal Assessment Report' on the substance.
An overview of the skeletal malformations can be found in Table 5 in 'Any other information on results incl. tables'.

Visceral malformations:

effects observed, non-treatment-related

Description (incidence and severity):

Visceral malformations were seen in one 10 mg/kg litter (hydrocephalus), in one 75 mg/kg litter (unilateral renal and ureteral aplasia), and in one 125 mg/kg litter (unilateral renal and bilateral ureteral aplasia).
Two anomalies were seen: small gall bladder in one 10 mg/kg foetus, and small liver in one 125 mg/kg foetus.
Because of their low incidence, lack of dose-relationship, and occurrence in historical control data, these findings were not regarded as treatment related. There were no other remarkable visceral observations in the study.
An overview of the visceral malformations can be found in table 4 in 'Any other information on results incl. tables'.

Other effects:

effects observed, treatment-related

Description (incidence and severity):

EXTERNAL ANOMALIES:
The foetal incidence of position anomaly of one or both forelimbs was dose-relatedly increased, and was significantly higher than controls in the 125 mg/kg group. This was considered to be a treatment effect. The finding consists of flexure of the forepaw at the wrist; it is most likely due to restriction of movement in the uterus; in absence of related morphological findings, it is not categorised as a malformation.
An overview of the external anomalies can be found in table 4 in 'Any other information on results incl. tables'.

SKELETAL ANOMALIES:
- In the 125 mg/kg group, there was an increased incidence of fused sternebrae (2-3, 3-4, 4-5).
- In the 125 and 75 mg/kg groups, there was a dose-related increase in reduced pubis.

SKELETAL VARIATIONS:
Variations occurred in almost all litters. The most frequent variations seen in this study were poor or absent ossification of sternebra-5 and caudal vertebral centers. The following were regarded as treatment-related:
- in the 125 mg/kg group, an increased incidence of poor ossification of metacarpal-1, talus, and medial phalanx of anterior digit-5, and additional caudal vertebral centers.
- in the 125 and 75 mg/kg groups, a dose-related increase in incidence of additional 13th rib(s).
An overview of skeletal anomalies and variations can be found in Table 5 in 'Any other information on results incl. tables'.

Effect levels (fetuses)

Key result

Dose descriptor:

NOAEL

Effect level:

10 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

female

Basis for effect level:

reduction in number of live offspring

external malformations

skeletal malformations

Fetal abnormalities

Key result

Abnormalities:

effects observed, treatment-related

Localisation:

skeletal: supernumerary rib

skeletal: pelvic girdle

Description (incidence and severity):

No indication of severity givin by the authors

Overall developmental toxicity

Key result

Developmental effects observed:

yes

Lowest effective dose / conc.:

75 mg/kg bw/day (actual dose received)

Treatment related:

yes

Relation to maternal toxicity:

developmental effects as a secondary non-specific consequence of maternal toxicity effects

Dose response relationship:

yes

Relevant for humans:

yes

Any other information on results incl. tables

ANALYTICAL VERIFICATION OF DOSES:

The results obtained for the content, homogeneity and stability of the test substance in bidistilled water with 0.5% CMC are summarized below:

- The mean concentrations of the homogeneity samples were found to be in the range from 82.4% to 101.6% of the nominal concentrations.

- The homogeneity varied in the range from -2% to +4% of the mean concentrations.

- The test substance was found to be stable in bidistilled water with 0.5% CMC at room  temperature for the period of dosing.

Table 1. calculation of corrected body weight gain of dams (day 6 to day 21 p.c.)

Parameter / dose	0 mg/kg	10 mg/kg	75 mg/kg	125 mg/kg
Number of dams	16	17	17	13
Body weight (g); day 0	2382 d	2358	2373	2355
Body weight (g); day 29	2633 d	2647	2562	2501 *
Body weight gain (g), day 7 to 19	87 d	92	33 *	-29 **
Body weight gain (g), day 0 to 29	251 d	289	189	146
Mean gravid uterus weight [g]	348	345	334	282
Mean carcass weight [g]	2284	2302	2228	2219

d = ANOVA; Dunnet-Test: 5 % (*) or 1 % (**) level

Table 2. fertility data

Parameter / dose	0 mg/kg	10 mg/kg	75 mg/kg	125 mg/kg
Females assigned	20	20	20	20
Dams pregnant	16	17	18	16
Dams with live fetuses on day 29	16	17	17	13
Dams with total resorptions	0	0	1	3
Dams delivering early	0	0	0	0
Dams aborting	0	0	0	1

Table 3. Caesarean section data

	Group	Group 1	Group 2	Group 3	Group 4
	Group name	Control	Low dose	Mid dose	High dose
	Dose level	0 mg/kg	10 mg/kg	75 mg/kg	125 mg/kg
Pregnant, used for calculation	n	16	17	18	16
No. of corpea lutea per animal	mean	8.3	9.0	8.8	7.8
No. of implantation sites per animal	mean	6.8	7.2	6.9	6.3
% of preimplantation loss per animal	mean	20.3	20.5	22.0	20.5
No. of foetuses per animal	mean	6.4	6.8	6.1	4.5
-% of which alive		100	100	100	100
-% of which dead		0	0	0	0
No. of early resorptions per animal	mean	0.3	0.4	0.8	1.8
No. of early resorption as % of implantation per animal	mean%	3.1	5.6	12.4	26.3
No. of early+late resorptions per animal	mean	0.3	0.4	0.8	1.8
No. of early+late resorption as % of implantation per animal	mean%	7.0	9.6	24.6	42.7
No. of postimplantation loss per animal	mean	0.3	0.4	0.8	1.8
No. of postimplantation loss as % of implantation per animal	mean%	7.0	9.6	24.6	42.7

Table 4. fetal external and visceral data 

Foetal Data - External and Visceral Examination (No. of foetuses / No. of litters affected)
Observation	0 mg/kg	10 mg/kg	75 mg/kg	125 mg/kg
Foetuses evaluated / Litters evaluated	103 / 16	116 / 17	110 / 17	72 / 13
Total external abnormalities	0 / 0	1 / 1	4 / 2	6** / 4
- position anomaly forelimb (A, 1)	0 / 0	1 / 1	4#/ 2	6**#/ 4
Total visceral malformations/abnormalities	0 / 0	3 / 2	1 / 1	2 / 2
- domed head (A)	0 / 0	1 / 1	0 / 0	0 / 0
- external hydrocephalus (M)	0 / 0	2 / 1	0 / 0	0 / 0
- internal hydrocephalus (M)	0 / 0	1 / 1	0 / 0	0 / 0
- small gall bladder (A)	0 / 0	1 / 1	0 / 0	0 / 0
- small liver (A)	0 / 0	0 / 0	0 / 0	1 / 1
- renal aplasia (M)	0 / 0	0 / 0	1 / 1	1 / 1
- ureter aplasia (M)##	0 / 0	0 / 0	1 / 1	1 / 1

M= malformation, A = Anomaly, 1 = flexure of the forepaw at the wrist,

Chi-square + fisher’s exact: ** = p< 0.01;

# also increased in comparison to historic controls; ## not observed in historic controls

 Table 5. skeletal examination data

Foetal Data - Skeletal Examination (No. of foetuses / No. of litters affected)
Observation	0 mg/kg	10 mg/kg	75 mg/kg	125 mg/kg
Foetuses evaluated / Litters evaluated	103 / 16	116 / 17	110 / 17	72 / 13
Total Malformations	0 / 0	0 / 0	0 / 0	0 / 0
Total Mean Anomalies	11 / 7	23 / 12	15 / 8	28*# / 11
- fused sternebrae 2-3	0 / 0	0 / 0	0 / 0	6**#/ 2
- fused sternebrae 3-4	5 / 4	6 / 3	3 / 3	18**#/ 8
- fused sternebrae 4-5	2 / 2	7 / 6	4 / 3	19**#/ 8
- reduced pubis###	0 / 0	0 / 0	2##/ 2	3##/ 2
Total Variations	80 / 16	95 / 17	90 / 17	67 / 13
- additional caudal vertebral centers	14 / 10	17 / 10	21 / 13	31**/10
- additional rib 13	2 / 2	2 / 2	11*/ 6	21**#/ 7
- poor ossification of metacarpal-1 (1	1 / 1	2 / 2	2 / 2	10**/ 5
- poor ossification of talus (1	1 / 1	2 / 1	3 / 2	8**/ 4
- poor ossif. of medial phalanx of anterior digit-5 (1	9 / 6	19 / 11	14 / 9	22**/ 9

(1 = common variation normally indicating a slight delay in foetal development / ossification chi-square + fisher’s exact: ** = p< 0.01, * = p< 0.05;

# also increased in comparison to historic controls, ## not observed in historic controls

###Reduced pubis was reported as an anomaly in the report, but is considered to be a malformation according to the 'Renewal Assessment Report' on the substance

Applicant's summary and conclusion

Conclusions:

- Maternal toxicity (reduced feed consumption and body weight gain; two deaths at 125 mg/kg) and increased post-implantation losses and fetal anomalies and variations consistent with delayed development were seen in the 75 and 125 mg/kg groups.
- The No Observed Adverse Effect Level (NOAEL) for rabbit dams and foetuses in this study was 10 mg/kg.
- There was no evidence for teratogenicity.

Executive summary:

In a GLP compliant teratogenicity study, performed in accordance with OECD 414, the test substance was tested for its embryonic, foetotoxic, and teratogenic potential in rabbits. The test material was administered by gavage in an aqueous solution of carboxymethylcellulose (0.5% w/w) at daily doses of 0, 10, 75 and 125 mg/kg body weight to 20 inseminated Russian Chbb:HM rabbits per group from day 7 to 19 of pregnancy inclusive, using a dose volume of 4 mL/kg body weight. Dams were killed on day 29 of pregnancy, just prior to the expected delivery and foetuses were removed by Caesarean section for subsequent external, visceral and skeletal examination.

One dam in the control group died on day 16. Two dams in the 125 mg/kg group died on day 16 and 17 respectively. Another dam in the highest treatment group was sacrificed after abortion on day 19. The deaths in the 125 mg/kg group were presumed to be treatment-related. Mean body weights were dose-relatedly reduced in the 75 and 125 mg/kg groups, compared to controls. At 75 mg/kg, mean maternal body weight gain was reduced from days 7 to 19, achieving 38% of the control value. At 125 mg/kg, there was even a loss of mean body weight, particularly from days 16 to 20. Body weights and body weight gain were unaffected by treatment in the 10 mg/kg group. Feed consumption was significantly and dose-dependently reduced in the 75 and 125 mg/kg groups during the treatment period (days 7 to 19 of pregnancy). Gross pathological examination of the dams did not reveal findings which are uncommonly observed at necropsy. The findings in the high dose animals can therefore not be attributed with any certainty to the treatment.

Preimplantation losses did not differ between groups. Post-implantation losses were dose-dependently increased in the 75 and 125 mg/kg groups and were based on early resorptions. Additionally, at the highest dosage group, one abortion and three completely resorbed litters were recorded. Mean litter size was reduced at 125 mg/kg bw/day. Foetal body weights were not affected. The total number of external abnormalities is significantly higher in the group receiving the highest dosage (6/72 foetuses compared with 0/103 foetuses in the control group). The foetal incidence of forelimb position anomalies was increased in the 125 mg/kg group. There were no treatment-related visceral or skeletal malformations. Incidence of the following skeletal findings was increased in the 125 mg/kg group: fused sternebrae (anomaly), reduced pubis (reported by the authors as anomaly, but considered a malformation by the 'Renewal Assessment Report' on the substance), 13thribs (variations), poor ossification of metacarpal-1, talus, and medial phalanx of anterior digit-5 (variations). In the 75 mg/kg the following skeletal finding were observed: reduced pubis (reported by the authors as anomaly, but considered a malformation by the 'Renewal Assessment Report' on the substance) and 13thribs (variation). Maternal toxicity (reduced feed consumption and body weight gain; two deaths at 125 mg/kg) and increased post-implantation losses and foetal anomalies and variations consistent with delayed development were seen in the 75 and 125 mg/kg groups. The No Observed Effect Level (NOAEL) for rabbit dams and foetuses in this study was 10 mg/kg. There was no evidence for teratogenicity.