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Toxicological information

Developmental toxicity / teratogenicity

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Administrative data

developmental toxicity
Type of information:
experimental study
Adequacy of study:
key study
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference Type:
study report
Report date:

Materials and methods

Test guideline
according to guideline
OECD Guideline 414 (Prenatal Developmental Toxicity Study)
GLP compliance:
Limit test:

Test material

Constituent 1
Chemical structure
Reference substance name:
Butanone oxime
EC Number:
EC Name:
Butanone oxime
Cas Number:
Molecular formula:
Test material form:

Test animals

Details on test animals or test system and environmental conditions:
- Source: Charles River Laboratories, Inc., Kingston, NY
- Age at study initiation: 90 days old
- Weight at study initiation: 222 - 291 g
- Housing: Individually in wire-mesh stainless steel cages
- Diet (e.g. ad libitum): Purina Certified Rodent Meal No. 5002
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 13 days prior to mating

- Temperature (°C): 17.7 - 26.1
- Humidity (%): 64-70
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:
oral: gavage
Details on exposure:
Dosage solutions were administered orally by gavage as a single dose daily from gestation day 6 through gestation day 15. Individual doses were calculated using the most recent body weight data. Dose levels were 0 (distilled water control), 60, 200 or 600 mg MEKO/kg body weight. The dose volume was 10 mL/kg.

Analytical verification of doses or concentrations:
Details on analytical verification of doses or concentrations:
The test substance, MEKO, was analyzed for purity and the test solutions were analyzed for homogeneity and stability by a gas chromatographic
procedure using a Poropack P column and a flame ionization detector. Overall the material used was > 99% pure and recoveries were ~ 99-100%.
Stability over the course of the dosing period was > 93%.
Details on mating procedure:
Selected females were cohabitated with male rats of the same strain and source. Evidence of mating was determined by the presence of a copulatory plug in the vagina or a sperm positive vaginal smear. The day evidence of copulation was observed was designated day 0 of gestation and the female rats were assigned consecutively, in a block design, to study groups.
Duration of treatment / exposure:
Gestation Days 6-15.
Frequency of treatment:
Duration of test:
Until sacrifice on Gestation Day 20.
Doses / concentrationsopen allclose all
Dose / conc.:
60 mg/kg bw/day (actual dose received)
Dose / conc.:
200 mg/kg bw/day (actual dose received)
Dose / conc.:
600 mg/kg bw/day (actual dose received)
No. of animals per sex per dose:
25 females/dose
Control animals:
yes, concurrent vehicle
Details on study design:
- Dose selection rationale: Dose levels for this rat developmental toxicity studies were based on results of a range finding study in which groups of 6 pregnant rats received MEKO at levels of 25, 100, 200 or 400 mg/kg bw/day on gestation days 6-15. Hematological status was evaluated by measuring methemoglobin and reticulocyte levels. Mothers were sacrificed on gestation day 20 for Cesarean ection evaluations. Fetal evaluations in the range finding study were limited to external observations. All dams survived treatment. Clinical signs of toxicity were observed at 400 mg/kg bw/day including transient central nervous system depression. Dose-related increases in the levels of reticulocytes and methemoglobin occurred at all dose levels throughout gestation. Methemoglobin levels at 400 mg/kg bw/day were as high as 39%. Enlarged black/purple spleens were found at dose levels of 100 mg/kg bw/day and above. These effects suggested anemia was induced by the treatment. No adverse effects on gestational parameters such as the number of resorptions, viable fetuses and fetal weights were found. No fetal external malformations or developmental variations were observed. Statistical analyses were not performed in the range finding study.


Maternal examinations:
- During the experimental period, all animals were observed daily for clinical signs of toxicity including physical or behavioral abnormalities.
- Mortality checks were perfomed twice daily, in morning and afternoon.
- During the dosing period, the females were observed between one-half hour and two hours following dosing for overt signs of toxicity.
- Body weights of individual animals were measured and recorded on gestation days 0, 6, 9, 12, 16 and 20. Body weight changes were calculated for the following gestation intervals: 0.-6, 6-9, 9-12, 12-16, 16-20, 6-16 and 0-20.
- Food consumption was measured (as g/animal/day and g/kg/day) during gestation days 0-6, 6-9, 9-12, 12-16 and 16-20.
Ovaries and uterine content:
After sacrifice on day 20, the uterus was removed from the body, examined externally, weighed, and then opened fo an internal examination. The number of viable and nonviable fetuses, early and late resorptions was recorded beginning with the left distal uterine horn, noting the position of the cervix, and continuing with the right uterine horn. Corpora lutea were counted and recorded for each ovary. Uteri with no macroscopic evidence of implants were placed in 10% aqueous ammonium sulfide for detection of early embryolethality.
Fetal examinations:
Fetuses were examined for external, visceral and skeletal abnormalities. Developmental malformations and variations were classfied based on the severity of the anatomical change(s) and their potential interference with organ and/or body functions.
Statistical analyses were performed by a Digital Vax 11/730 computer. All analyses were two-tailed with a minimal significance level of 5%. One-way analysis of variance followed by Dunnett's test was used to analyze maternal and fetal data including body weights, food consumption, number of viable fetuses, implantation sites, and corpora lutea. The Mann-Whitney U test was used to compare post-implantation loss, dead fetuses, and resorptions. Fetal sex ratios were analyzed using the Chi-Square test. Fisher's Exact test was used to analyze the incidence and number of fetal malformations. and variations utilizing the dam (litter) as the experimental unit.

Results and discussion

Results: maternal animals

General toxicity (maternal animals)

Clinical signs:
effects observed, treatment-related
Description (incidence and severity):
Clinical signs of toxicity were observed at 200 and 600 mg/kg bw/day. These clinical signs (signs of general nervous system depression) were generally transient and had disappeared before dosing on the following day.
No treatment-related clinical signs were observed at the 60 mg/kg/day treatment level.
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
Body weight losses and/or reduced body weight gain were observed at 200 and 600 mg/kg bw/day.
Food consumption and compound intake (if feeding study):
effects observed, treatment-related
Description (incidence and severity):
Reduced food consumption was seen at 200 and 600 mg/kg bw/day.
Gross pathological findings:
effects observed, treatment-related
Description (incidence and severity):
Enlarged spleens were seen at necropsy in all MEKO-treated animals but not in the controls.

Effect levels (maternal animals)

open allclose all
Dose descriptor:
developmental toxicity
Effect level:
> 600 mg/kg bw/day (actual dose received)
Based on:
test mat.
Basis for effect level:
other: No treatment-related gestational effects, malformations or developmental variations at the highest dose level.
Dose descriptor:
general toxicity
Effect level:
60 mg/kg bw/day (actual dose received)
Based on:
test mat.
Basis for effect level:
gross pathology

Maternal abnormalities

no effects observed

Results (fetuses)

Details on embryotoxic / teratogenic effects:
Embryotoxic / teratogenic effects:no effects

Effect levels (fetuses)

Dose descriptor:
developmental toxicity
Effect level:
> 600 mg/kg bw/day (actual dose received)
Based on:
test mat.
Basis for effect level:
other: no adverse effects observed

Fetal abnormalities

no effects observed

Overall developmental toxicity

Developmental effects observed:

Applicant's summary and conclusion

Maternal oral exposure to methyl ethyl ketoxime (MEKO) at concentrations up to 600 mg/kg bw/day during gestation days 6 through 15 did not induce develpmental toxicity in rats. In this study, the NOEL for develpmental toxicity in the rat was 600 mg/kg bw/day. Maternal toxicity was noted in all MEKO treated rats (60, 120 and 600 mg/kg bw/day).