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Toxicological information

Toxicity to reproduction

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Administrative data

Endpoint:
screening for reproductive / developmental toxicity
Remarks:
based on test type (migrated information)
Type of information:
experimental study
Adequacy of study:
key study
Study period:
14 May - 28 August 2008
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
GLP study conducted according to OECD Guideline 421 with deviations: temperature and humidity were not recorded for 4 days. Temperature and humidity were sometimes out of the target range. Only 7/10 pregnant females in the control group (and 6 delivered litters).
Cross-referenceopen allclose all
Reason / purpose for cross-reference:
reference to same study
Reason / purpose for cross-reference:
reference to other study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2010
Report date:
2010

Materials and methods

Test guideline
Qualifier:
according to guideline
Guideline:
OECD Guideline 421 (Reproduction / Developmental Toxicity Screening Test)
Deviations:
yes
Remarks:
temperature and humidity not recorded for 4 days & sometimes out of target range. Only 7 pregnant females in contol group.
Principles of method if other than guideline:
Not applicable
GLP compliance:
yes
Limit test:
no

Test material

Constituent 1
Reference substance name:
Reference substance 001
Cas Number:
9022-76-8
Details on test material:
- Name of test material (as cited in study report): CHIMEXANE NB
- Physical state: Brownish viscous liquid
- Analytical purity: 97.3 %
- Lot/batch No.: 0129336
- Date of receipt: 27 February 2006 and 9 April 2008
- Expiration date of the lot/batch: September 2008
- Storage condition of test material: Room temperature

Test animals

Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Janvier, Le Genest-Saint-Isle, France.
- Age at study initiation: 11-12 weeks
- Weight at study initiation: Males: 392-453 g (mean 420 g); Females: 268-302 g (mean 285 g)
- Housing: Animals were housed individually in wire-mesh cages (43.0 x 21.5 x 18.0 cm); Towards the end of gestation and during lactation, the females were individually housed, and with their litter after birth, in polycarbonate cages (43.0 x 21.5 x 20.0 cm) containing autoclaved wood shavings (SICSA, Alfortville, France) as nesting material.
- Diet: A04 C powdered maintenance diet (SAFE, Augy, France) distributed weekly, ad libitum
- Water: Tap water (filtered with a 0.22 μm filter), ad libitum
- Acclimation period: 9 days

ENVIRONMENTAL CONDITIONS
- Temperature: 22 ± 2 °C
- Humidity: 50 ± 20 %
- Air changes: Approximately 12 cycles/h of filtered, non-recycled air
- Photoperiod: 12 h dark / 12 h light

Administration / exposure

Route of administration:
oral: feed
Vehicle:
other: dietary admixture, in A04 C powdered maintenance diet
Details on exposure:
DIET PREPARATION
- For each concentration, a premix with the total amount of test item was prepared in the diet using a mixer. The final mix was prepared by dispersing the premix in the remaining diet in the mixer and then mixing for at least 10 minutes. Control animals were offered untreated diet alone.
- Storage temperature of food: Dietary admixtures were prepared on a weekly basis and were stored in closed bags at room temperature and protected from light prior to use.

STABILITY
- Satisfactory homogeneity and stability of dietary admixtures prepared at 500 or 20000 ppm was demonstrated during the study (Study No. 34827 AHS), over an 8-day storage period in open feeders and after 14 days of storage in closed bags at room temperature.
Details on mating procedure:
- M/F ratio per cage: 1:1
- Length of cohabitation: 1-14 days
- Proof of pregnancy: Presence of vaginal plug / sperm in vaginal lavage referred to as Day 0 post-coitum (p.c.).
- Pre-coital time was calculated for each female.
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
- Concentration of the test item in samples of each control and test item dietary admixtures prepared for use in Weeks 1, 4 and 8 was determined. On each day of analysis, duplicate samples was taken at three different levels (top, middle, bottom) of the mixer (groups 2, 3 and 4) or at a single level of the container (control group) for the determination of the test item concentration.
- Acceptance criterion: Measured concentration = nominal concentration ± 20 %.

Results: Test concentrations in the administered dietary admixtures analyzed remained within the acceptable range of -20 to -3 % of variation compared to the nominal values, except for highest dose group in Week 1 where the deviation from nominal value was -22 %.
Duration of treatment / exposure:
Males:
- 2 weeks before mating, during the mating (maximum of 2 weeks) and post-mating periods (at least 2 weeks) until sacrifice (at least 6 weeks in total).

Females:
- 2 weeks before mating, during the mating period (maximum of 2 weeks), during pregnancy and lactation, until Day 4 post-partum inclusive, (or until sacrifice for un-mated and non-pregnant females).
Frequency of treatment:
Once daily
Doses / concentrations
Remarks:
Doses / Concentrations:
Males: 2175, 6525 and 14500 ppm; Females: 1950, 5850 and 13000 ppm [target dose levels 150, 450 and 1000 mg/kg bw/day]
Basis:
nominal in diet
No. of animals per sex per dose:
10
Details on study design:
- Dose selection rationale: Dose levels were selected on the basis of the results of 4-week toxicity study (Study No. 31261 TSR) in which the test item was administered by dietary admixture at the target dose-levels of 150, 450 and 1000 mg/kg bw/day.
- Rationale for animal assignment: During the acclimation period, the required number of animals (40 males and 40 females) was selected according to body weight and/or clinical condition. They were then allocated to groups (by sex), using a stratification procedure based on body weight.
Positive control:
Not applicable

Examinations

Parental animals: Observations and examinations:
CAGE SIDE AND CLINICAL OBSERVATIONS: Yes
Time schedule:
- Morbidity and mortality: Once a day during the acclimation period and at least twice a day during the treatment period.
- Clinical signs: Once daily

BODY WEIGHT: Yes
Time schedule for examinations:
- Male: Once before group allocation, on the first day of treatment (Day 1), then once a week until sacrifice.
- Female: Once before group allocation, on the first day of treatment (Day 1), then once a week until mated (or until sacrifice) and on Days 0, 7, 14 and 20 p.c. and Days 1 and 5 post-partum.

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
Time schedule:
- Male: Once a week, over a 7-day period, from the first day of treatment until sacrifice.
- Female: Once a week, over a 7-day period, from the first day of treatment through gestation (Days 0-7, 7-14 and 14-20 p.c. intervals) and lactation (Days 1-5 post-partum interval) until sacrifice.
- During the mating period, the food consumption was noted for neither males nor females.
Compound intake calculated as time-weighted averages from the consumption and body weight gain data: Yes
- Achieved intake of the test item (in terms of mg/kg bw/day) was calculated on a weekly basis for each test item-treated group as follows:
D = C x FC/BW; where, D = achieved dosage (mg/kg bw/day), C = nominal concentration of active test item (ppm: mg test item/10^6mg food), FC = mean food consumption (g/animal/day), BW = mean body weight (g)

PARTURITION:
- Females were allowed to litter normally and rear their progeny until Day 5 post-partum inclusive. Any sign of a difficult or prolonged parturition was recorded. The day of completed parturition was designated Day 1 post-partum. The length of gestation was calculated.
Oestrous cyclicity (parental animals):
Estrous cycle stage was recorded daily until the female was positive for mating.
Sperm parameters (parental animals):
Parameters examined in male animals:
- Testes and epididymis (total and cauda weight) weight were recorded.
Litter observations:
LITTER SIZE
- Total litter size and numbers of pups of each sex were recorded as soon as possible after birth.
- Litters were observed daily for recording of the number of live, dead and cannibalized pups.
- External examination of each pup was carried out and any external malformation was noted.

CLINICAL SIGNS
- Pups were observed daily for recording of the clinical signs or abnormal behavior.

BODY WEIGHT
- Weight of each pup was recorded on Days 1 and 5 post-partum.
Postmortem examinations (parental animals):
SACRIFICE: On completion of the treatment period, all animals were deeply anesthetized by an intraperitoneal injection of sodium pentobarbital and sacrificed by exsanguination.
- Males : All surviving animals were sacrificed after delivery of the majority of the females per group.
- Females: All surviving animals [on Day 5 post-partum, 24-26 days after the last day of the mating period for the females which did not mate, on or after Day 25 post-coitum for the females which had not delivered by Day 25 p.c.]

GROSS NECROPSY
- Macroscopic post-mortem examination of the external surfaces, all orifices, cranial cavity, external surfaces of the brain, thoracic, abdominal and pelvic cavities with their associated organs and tissues and the neck with its associated organs and tissues.
- In all females, the number of implantation sites and corpora lutea was recorded.
- In the females which did not mate or were apparently non-pregnant, the presence of implantation sites on the uterine horns was checked using ammonium sulphide staining technique.

ORGAN WEIGTHS
- Epididymides (total and cauda weight), ovaries (with oviducts), prostate, seminal vesicles (with coagulating glands and their fluids) and testes were weighed.
- Ratio of organ weight to body weight (recorded immediately before sacrifice) was calculated.

HISTOPATHOLOGY
- Microscopic examination was performed on the macroscopic lesions, ovaries, testes and epididymides (with special emphasis on stages of spermatogenesis and histopathology of interstitial testicular cell structure) in all males and females of the control and high-dose groups.
- See table 7.8.1/1
Postmortem examinations (offspring):
SACRIFICE:
- Pups were sacrificed on Day 5 post-partum, by intraperitoneal injection of thiopental sodium.

GROSS NECROPSY
- Macroscopic examination was performed for all pups, including those found dead or prematurely sacrificed.
- Macroscopic lesions were preserved in 10 % buffered formalin (or another appropriate fixative) and were not microscopically examined in a first instance.
Statistics:
- Data other than organ weights: Mean values were compared by one-way analysis of variance and the Dunnett test (mean values being considered as normally distributed and variances being considered as homogeneous). Percentage values were compared by the Fisher exact probability test.
- Organ weights: PathData software (version 6.2b5) was used for the statistical analyses of organ weight data with a level of significance of 0.05 or 0.01.
Reproductive indices:
- Pre-implantation loss: [(Number of corpora lutea - Number of implantation sites) / Number of corpora lutea] X 100
- Post-implantation loss: [(Number of implantation sites - Number of live concepti) / Number of implantations] X 100
- Mating index: [Number of mated animals / Number of paired animals] X 100
- Fertility index: [Number of pregnant female partners / Number of mated pairs] X 100
- Gestation index: [Number of females with live born pups / Number of pregnant females] X 100
Offspring viability indices:
- Live birth index: [Number of live born pups / Number of delivered pups] X 100
- Viability index on Day 4 post-partum: [Number of surviving pups on Day 4 post-partum / Number of live born pups] X 100

Results and discussion

Results: P0 (first parental generation)

General toxicity (P0)

Clinical signs:
no effects observed
Body weight and weight changes:
no effects observed
Food consumption and compound intake (if feeding study):
no effects observed
Organ weight findings including organ / body weight ratios:
no effects observed
Histopathological findings: non-neoplastic:
no effects observed
Other effects:
no effects observed

Reproductive function / performance (P0)

Reproductive function: oestrous cycle:
no effects observed
Reproductive performance:
no effects observed

Details on results (P0)

MORTALITY (PARENTAL ANIMALS)
- No unscheduled deaths occurred during the study.

CLINICAL SIGNS (PARENTAL ANIMALS)
- No clinical signs were observed except the cutaneous lesion on the neck in one male at 450 mg/kg bw/day, however, this sign was not attributed to treatment with the test item.

BODY WEIGHT (PARENTAL ANIMALS)
- At 1000 mg/kg bw/day, lower body weight gain was observed in males and females during the first week of the pre-mating period (males: +28 g vs.+39 g; females: +13 g vs. +20 g) and the overall body weight gain of males from Day 1 to Day 43 was also lower than that of controls but not statistically significantly different. It was considered that these differences, which did not correlate with unaffected food consumption of this group, were no indicative of a test item treatment-related effect.
- During the gestation and lactation periods the body weight gain of test item-treated females was considered to be similar to that of controls.

FOOD CONSUMPTION (PARENTAL ANIMALS)
- Food consumption was unaffected by the treatment.

TEST SUBSTANCE INTAKE (PARENTAL ANIMALS)
- Mean achieved dosages increased in a near dose-proportional manner and mean values were close to the targeted dose-levels of 150, 450 and 1000 mg/kg bw/day.
- See table 7.8.1/2.

REPRODUCTIVE FUNCTION: ESTROUS CYCLE (PARENTAL ANIMALS)
- Estrous cycle was not affected by treatment with the test item at any dose level.

REPRODUCTIVE PERFORMANCE (PARENTAL ANIMALS)
Mating data:
- No effect of treatment on mating parameters at any dose-level.

Fertility data:
- All the mated females were pregnant except 2/9 and 1/9 females at control and 450 mg/kg bw/day, respectively.
- One control female was sacrificed on Day 27 p.c. because of absence of delivery but had one implantation site at hysterectomy; all other pregnant females had live pups. The female fertility index was therefore considered not to have been affected by treatment with the test item as the incidence of non-pregnant females was not dose-related.

Delivery data:
- Mean duration of gestation, mean numbers of corpora lutea, implantations and pups born, as well as the pre- and post-implantation losses, were all comparable with the controls for all groups treated with the test item.
- Post-implantation loss was slightly higher at 1000 mg/kg bw/day when compared with controls (16 % vs. 12.9 %). This increase was attributed to one female which had a post-implantation loss of 56.3 % and was considered to be of no toxicological significance.

ORGAN WEIGHTS (PARENTAL ANIMALS)
- Organ weight changes were considered not to be related to the test item as they were small in amplitude, had no gross or microscopic correlates, were not dose-related in magnitude, and/or were not consistent for the sexes.
- Seminal vesicle weights for one high-dose male were low (1.2910 g and 0.22441 g respectively for absolute and relative weights versus 1.84 g and 0.32108 g respectively for control mean absolute and relative weights). These low weights correlated with the reduced size of the left vesicle noted at necropsy and with decreased glandular content at microscopic examination. Since this finding was unilateral and isolated, it was considered to be incidental and unrelated to the test item.

GROSS PATHOLOGY (PARENTAL ANIMALS)
- All macroscopic findings were those commonly recorded in the Sprague-Dawley rats and none were considered to be related to the test item administration.

HISTOPATHOLOGY (PARENTAL ANIMALS)
- All microscopic findings noted in treated animals were considered to be incidental changes as they also occurred in controls, were of low incidence, had no dose-relationship in incidence or severity and/or are common background findings for the species.

Effect levels (P0)

Dose descriptor:
NOAEL
Effect level:
1 000 mg/kg bw/day (nominal)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: No mortality, no clinical signs, no effects on body weight or food consumption and no adverse effects on reproductive performance were observed at any of the doses tested.

Results: F1 generation

General toxicity (F1)

Clinical signs:
effects observed, treatment-related
Mortality / viability:
mortality observed, treatment-related
Body weight and weight changes:
no effects observed
Organ weight findings including organ / body weight ratios:
not examined
Gross pathological findings:
no effects observed

Details on results (F1)

VIABILITY AND CLINICAL SIGNS (OFFSPRING)
- Pup mortality was higher at 450 and 1000 mg/kg bw/day (9.5 and 17.6 %, respectively, vs. 0 % in controls) when compared to the controls. In the high-dose group, the entire litter of one dam was died and ante-mortem signs of paleness and/or coldness to the touch were noted. Pup mortality and clinical signs recorded at 450 and 1000 mg/kg bw/day were treatment-related.
- At 150 mg/kg bw/day, no clinical signs were observed and the mortality of pups was very low and considered not to be related to the test item treatment.

BODY WEIGHT (OFFSPRING)
- Body weight gain of male and female pups from the test item-treated groups was similar to that of the control group.

SEX RATIO (OFFSPRING)
- Percentage of male pups ranged between 42.6 and 56.2 % on Days 1 and 5 post-partum which was considered to be within the normal range.

GROSS PATHOLOGY (OFFSPRING)
- No findings were observed in the pups sacrificed on Day 5 post-partum.

Effect levels (F1)

Dose descriptor:
NOAEL
Generation:
F1
Effect level:
150 mg/kg bw/day (nominal)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: see 'Remark'

Overall reproductive toxicity

Reproductive effects observed:
not specified

Any other information on results incl. tables

Table 7.8.1/2: Achieved dosages

Mean achieved dosages (mg/kg bw/day) in males

Concentration (ppm)

2175

6525

14500

Pre-mating (Days 1-15)

141

388

938

Comparison with target dose-levels (%)

-6

-14

-6

Mean achieved dosages (mg/kg bw/day) in females

Concentration (ppm)

1950

5850

13000

Pre-mating (Days 1-15)

141

450

1094

Gestation (GD 0-20)

143

473

1044

Lactation (Days 1-5 p.p.)

208

511

1432

Overall mean (females)

164

478

1190

Comparison with target dose-levels (%)

+9

+6

+19

 

GD: Gestation Day, p.p.: post-partum

Table 7.8.1/3: Reproductive data

Dose-level (mg/kg bw/day)

0

150

450

1000

Summary of mating data

Paired males + females

10 + 10

10 + 10

10 + 10

10 + 10

Mating index (%)

90

80

90

100

Mean pre-coital time (days)

3.8

4.9

3.6

3.3

Fertility data

Fertility index (%)

77.8

100

88.9

100

Gestation index (%)

85.7

100

100

100

Delivery data

Litters with live born pups

6

8

8

10

Duration of gestation (days)

21.8

22.0

21.9

22.1

Mean number of corpora lutea

18.7

16.9

17.3

17.5

Mean number of implantations

17.0

16.3

16.3

16.2

Mean pre-implantation loss (%)

7.5

3.5

5.7

6.9

Mean number of pups delivered

14.8

14.8

14.5

13.6

Live birth index (%)

100

100

100

100

Mean post-implantation loss (%)

(calculated manually)

12.9

9.2

11.0

16.0

 

Table 7.8.1/4: Pup mortality and clinical signs

Dose-level (mg/kg bw/day)

0

150

450

1000

Pup mortality

between Days 1 and 4 p.p.

0 (0 %)

3 (2.5 %)

11** (9.5 %)

24 # (17.6 %)

Viability index on day 4 p.p.(%)

100.0

97.5

90.5

82.4

litters affected

0/6 (0 %)

2/8 (25 %)

4/8 (50 %)

6/10 (60 %)

Clinical signs

coldness to toucha

0/2

0/0

2/2

11/13

palenessa

0/2

0/0

2/2

2/13

Total litters affected by clinical signs

0/6 (0 %)

0/8 (0 %)

1/8 (13 %)

3/10 (30 %)

 

p.p.: post-partum, **: p<0.01; #: p<0.001, a: number of pups affected compared with the total of pups showing signs.

Applicant's summary and conclusion

Conclusions:
Under the test conditions, the No Observed Adverse Effect Level (NOAEL) of CHIMEXANE NB was considered to be 1000 mg/kg bw/day (concentration of 14500 ppm for the males or 13000 ppm for the females).
At 450 and 1000 mg/kg bw/day, the viability index on Day 4 p.p was lower than that of controls (90.5 and 82.4 %, respectively, vs.100.0 % in controls; statistically significant but within the historical range provided by the laboratory - 80.3 -100%). Data from this study, escpecialy the pups mortality reported at top dose, were reviewed by an Expert and compared to historical control data provided by the laboratory. The lower viability observed at the high dose was considered within the scope of biological variability of this species and strain.

Therefore, for embryo-fetal / pup developmental toxicity up to day 5 post-partum, the No Observed Adverse Effect Level (NOAEL) was considered to be at 1000 mg/kg/day.

Executive summary of the Expert Report

• Data from Reproduction/Developmental Toxicity Screening Test on Chimexane NB were reviewed and compared to contemporaneous control data (from a similar screening study) and historical control data provided by the CRO
• Control data in this screening study is not representative of expected (historical control) values as the small sample size determined by the study design (OECD 421) has been further reduced by one non-mated female, two non-pregnant and one total pre-partum litter loss, resulting in only 6 litters for evaluation, reducing the power of the study to detect adverse effects in treated groups. Data from the treated groups has therefore been compared to contemporaneous control data and a broad range of historical control values which provide insight into the biological variation expected in this species and strain
• Data for the high dose group include one animal which had total litter loss by day 2 post-partum. This is known to occur spontaneously and has been observed in a control animal in one of the 11 studies provided as historical data. There is no data to suggest that this animal was unduly sensitive to the test article and as the only recorded effect on pups was ‘cold to touch’ the deaths were considered secondary to poor maternal care
• As no other parameters on this study showed any treatment-related effects and as there were no effects indicating a potential mode of action observed in other toxicity studies with Chimexane NB (Prenatal Developmental Toxicity, 90-day Repeat Dose Toxicity, Genotoxicity), it was concluded that this effect was unlikely to represent reproductive or developmental toxicity
• Toxicity studies (Reproduction/Developmental Toxicity Screening Test, Prenatal Developmental Toxicity Study, 90-day Repeat Dose Toxicity Study) with the structurally similar compound Chimexane NC also show no adverse effects on reproduction or development and are considered to contribute to the weight of evidence for no effect on reproductive or developmental toxicity
• The lower viability observed in the high dose group of the Chimexane NB Reproduction/Developmental Toxicity Screening Test was considered, within the limitations of the study design, to be within the scope of biological variability of this species and strain rather than a definitive effect on reproductive function or developmental parameters, and this isolated finding is therefore unlikely to be a cause for concern
Executive summary:

In a reproduction/developmental toxicity screening study performed according to OECD Guideline 421 and in compliance with GLP, CHIMEXANE NB was administered by dietary admixture to groups (10/sex/dose) of Sprague-Dawley, Rj Han: SD rats at the dose levels of 0, 2175, 6525 and 14500 ppm for the males and 0, 1950, 5850 and 13000 ppm for the females (equivalent to target dose-levels of 0, 150, 450 and 1000 mg/kg bw/day) for 15 days before mating, through the mating and post-mating periods until sacrifice for the males, and through gestation and the beginning of the lactation period (until Day 4 post-partum (p.p.) inclusive) for the females. Clinical signs and mortality were checked daily. Body weight and food consumption were recorded at designated intervals throughout the study, except during the mating period when the food intake was not recorded. After 15 days of dosing, the males and females were paired and the females were allowed to litter normally and rear their progeny until Day 5 p.p. Males were sacrificed approximately 2 weeks after the end of the mating period, females on Day 5 p.p. The animals were sacrificed and subjected to a complete macroscopic examination and designated organs were weighed and examined microscopically. The pups were observed daily for clinical signs, sexed and weighed on Days 1 and 5 p.p and sacrificed on Day 5 p.p., and subjected for macroscopic examination.

 

No mortality and no clinical signs attributed to treatment with the test item were observed. No effects on body weight or food consumption were observed. The reproductive performance of males and females, mating, fertility, gestation and live birth indices were similar to that of the control group. No treatment-related effects were noted on testis or epididymis weights and no treatment-related findings were recorded at necropsy or microscopic examination of the testes, epididymides or ovaries in treated rats. There were no treatment-related effects on pup mortality, clinical signs or body weight at 150 mg/kg bw/day. At 450 and 1000 mg/kg bw/day, the viability index on Day 4 p.p was lower than that of controls (90.5 and 82.4 %, respectively, vs.100.0 % in controls; statistically significant but within the historical range provided by the laboratory - 80.3 -100%). No macroscopic findings were observed in the pups sacrificed on Day 5 post-partum.

Data from this study, escpecialy the pups mortality reported at top dose, were reviewed by an Expert and compared to historical control data provided by the laboratory. The lower viability observed at the high dose was considered within the scope of biological variability of this species and strain. Therefore, under the test conditions, the No Observed Adverse Effect Level (NOAEL) of CHIMEXANE NB was considered to be 1000 mg/kg bw/day (concentration of 14500 ppm for the males or 13000 ppm for the females) and 1000 mg/kg bw/day (overall mean achieved dosage 1190 mg/kg/day) for embryo-fetal / pup developmental toxicity up to day 5 post-partum, respectively in Sprague-Dawley rats

Executive summary of the Expert Report •Data from Reproduction/Developmental Toxicity Screening Test on Chimexane NB were reviewed and compared to contemporaneous control data (from a similar screening study) and historical control data provided by the CRO •Control data in this screening study is not representative of expected (historical control) values as the small sample size determined by the study design (OECD 421) has been further reduced by one non-mated female, two non-pregnant and one total pre-partum litter loss, resulting in only 6 litters for evaluation, reducing the power of the study to detect adverse effects in treated groups. Data from the treated groups has therefore been compared to contemporaneous control data and a broad range of historical control values which provide insight into the biological variation expected in this species and strain •Data for the high dose group include one animal which had total litter loss by day 2 post-partum. This is known to occur spontaneously and has been observed in a control animal in one of the 11 studies provided as historical data. There is no data to suggest that this animal was unduly sensitive to the test article and as the only recorded effect on pups was ‘cold to touch’ the deaths were considered secondary to poor maternal care •As no other parameters on this study showed any treatment-related effects and as there were no effects indicating a potential mode of action observed in other toxicity studies with Chimexane NB (Prenatal Developmental Toxicity, 90-day Repeat Dose Toxicity, Genotoxicity), it was concluded that this effect was unlikely to represent reproductive or developmental toxicity •Toxicity studies (Reproduction/Developmental Toxicity Screening Test, Prenatal Developmental Toxicity Study, 90-day Repeat Dose Toxicity Study) with the structurally similar compound Chimexane NC also show no adverse effects on reproduction or development and are considered to contribute to the weight of evidence for no effect on reproductive or developmental toxicity •The lower viability observed in the high dose group of the Chimexane NB Reproduction/Developmental Toxicity Screening Test was considered, within the limitations of the study design, to be within the scope of biological variability of this species and strain rather than a definitive effect on reproductive function or developmental parameters, and this isolated finding is therefore unlikely to be a cause for concern