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Toxicological information

Developmental toxicity / teratogenicity

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Administrative data

Endpoint:
developmental toxicity
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Study period:
1978
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable well-documented study report which meets basic scientific principles

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1978
Report Date:
1978

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 414 (Prenatal Developmental Toxicity Study)
Principles of method if other than guideline:
Conducted according to the Food and Drug Administration 1966 "Guidelines for Reproduction Studies for Safety Evaluation of Drugs for Human Use", Segment II (Teratological Study)
GLP compliance:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): MRD-77-44
- Physical state: Clear Colorless liquid

Test animals

Species:
rat
Strain:
Sprague-Dawley
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Bredding Laboratories
- Age at study initiation: females (58 days); males (sexually mature)

- Housing: individually except during mating
- Diet (e.g. ad libitum): ad libitum (food removed during exposure period)
- Water (e.g. ad libitum): ad libitum (water removed during exposure period)


Administration / exposure

Route of administration:
inhalation: vapour
Type of inhalation exposure (if applicable):
whole body
Details on exposure:
Appropriate amounts of test material were transferred from a reservoir using a metering pump into a heated flask and flash evaporated. A stream of clean air was also passed through the flask and the vapor laden air transferred to a port in the chamber air inlet, where it was diluted with normal chamber intake air to give the desired concentration. Adjustments in the exposure air concentration were made by changing the rate of the flow of test material through the metering pump.

The stainless steel and glass exposure chambers and an effective exposure volume of 760 liters. They were operated dynamically at a flow rate of approximately 125 liters per minute. This provided one air change every 8 minutes and a 99% equilibrium time of 39 minutes.

Atmospheric sampling was performed using a Wilks Scientific Corp Miran IA Ambient Air Analyzer (long pathlength infrared). The infrared spectrum of the test material was measured and a strong band associated with the test material was observed at 3.4 microns. Calibration curves relating the absorption at this wavelength to the airborne concentration of the test materials were prepared. On each exposure day, three samples were drawn from each exposure chamber and the exposure concentration calculated by comparing the absorption of this sample to the standard curve.

Postive control animals were treated via gastric intubation on gestational days 6-15 with 400mg/kg/day of acetylsalicylic acid in 0.5% methocel.
Analytical verification of doses or concentrations:
yes
Details on mating procedure:
All females selected for mating were places with male rats nightly in a 2:1 ratio. Vaginal smears were taken early in the morning and females were considered to have mated if sperm and/or a vaginal plug were observed. The day on which evidence of mating was first observed was established as Day 0 of gestation for that animal. Mated females were assigned to groups by daily body weight gain in an attempt to equalize Day 0 mean group body weights.
Duration of treatment / exposure:
Females were exposed on gestation days 6-15 by inhalation 6h/day
Frequency of treatment:
daily gestation days 6-15
Duration of test:
Day 6 of gestation ranged from 23 January-3 February 1978
Day 15 of gestation ranged for 1-12 February 1978
Doses / concentrationsopen allclose all
Remarks:
Doses / Concentrations:
300 ppm
Basis:
nominal conc.
Remarks:
Doses / Concentrations:
900 ppm
Basis:
nominal conc.
No. of animals per sex per dose:
Negative control (Chamber air)- 20 mated females
Postive control (acetylsalicylic acid)-20 mated females
300 ppm- 21 mated females
900ppm- 21 mated females

Control animals:
yes, sham-exposed
other: positive control treated with 400mg/kg/day acetylsalicylic acid

Examinations

Maternal examinations:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily


DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: daily


BODY WEIGHT: Yes
- Time schedule for examinations: Days 0, 6-15, and 21 of gestation



POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day # 21
- Organs examined: uterus (number and location recorded for each horn of the following: live fetuses, dead fetuses, late resorptions, early resorptions, implantation sites); ovaries (number of corpora lutea per ovary)


Fetal examinations:
All fetuses were weighted, crown-rump distance measured, examined externally for malformations and sex determined externally (anogenital distance)
- External examinations: Yes: [all per litter ]
- Soft tissue examinations: Yes
- Skeletal examinations: Yes: [2/3 of litter ]
Fetuses designated for skeletal evaluation were eviscerated prior to initiation of the skeletal staining procedure. During the evisceration step the visceral contents of the thoracic and abdominal cavities were evaluated grossly in situ and sex was determined by internal inspection of gonads. Examination of skeleton for anomalies and ossification variations was performed after staining.
- Neural and Visceral defects: Yes: [1/3 of litter]
Statistics:
Comparisons between the negative control and treated groups and between the negative control and positive control groups were made where applicable by the chi-square method. Body weights, body weight gains, numbers of corpora lutea, implantations, resorptions, fetuses per dam, fetal and litter weights and crown-rump distances were compared to control by the F-test and Student’s t-test. When variances differed significantly, Student’s t-test was appropriately modified using Cochran’s approximation.

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:
Maternal toxic effects:no effects

Details on maternal toxic effects:
Animals treated with 900 ppm exhibited a slight increase in excessive lacrimation during the treatment and post-treatment periods. This same group also exhibited an increased incidence of brown flakes in the fur covering the head area during the treatment period. Premature delivery of the litter on Day 21 of gestation prior to maternal sacrifice was observed in one negative control female, and two test material treated females. There were no remarkable gross postmortem changes in the treated adult females. All other physical observations occurred with similar frequencies in all groups and were considered to represent common observations noted in rats in the laboratory environment.

Positive control animals demonstrated statistically significant decreased body weight gain. Females had in utero litters containing fewer live fetuses and more resorption sites than untreated control litters. The implantation efficiency value was significantly reduced and the incidence of dams with two or more resorptions was increased.

Effect levels (maternal animals)

open allclose all
Dose descriptor:
NOAEL
Effect level:
>= 5 220 mg/m³ air (nominal)
Basis for effect level:
other: maternal toxicity
Dose descriptor:
NOAEL
Effect level:
>= 5 220 mg/m³ air (nominal)
Basis for effect level:
other: developmental toxicity

Results (fetuses)

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

Details on embryotoxic / teratogenic effects:
All fetal survival, size and sex data for groups treated with test material were considered comparable to negative control data. Slight delays or variation in the normal ossification process were observed in treated animals. However such variation are common as the time of normal ossification can vary and were comparable to the variation observed in the control animals. The incidence of fetuses with external malformations and incidences of litters containing malformed fetuses in the groups treated with test material were considered comparable to the control data. No significant difference in the incidence of visceral malformations was observed in the treated groups. The incidence of fetuses with soft tissue malformation in groups treated with test material was comparable to the negative control.

In the positive control group, the percentage of live fetuses and mean fetal size data were significantly lower than the negative control and the percentage of resorbed fetuses was significantly higher than control. The incidence of fetuses with ossification variation was significantly higher than the control value. The incidence of fetuses with soft tissue malformations was significantly higher in the positive control treated group than the negative control.

Fetal abnormalities

Abnormalities:
not specified

Overall developmental toxicity

Developmental effects observed:
not specified

Applicant's summary and conclusion

Conclusions:
There was no evidence of maternal or fetal toxicity at either exposure level of MRD-77-44 tested. Based on these results, both the maternal and developmental NOAELs were greater than or equal to 900 ppm (>= 5220 mg/m^3).
Executive summary:

MRD-77-44 was administered to pregnant female rats by inhalation exposure to vapor concentrations of 300 or 900 ppm, 6 hours/day during gestation days 6 to 15 to assess developmental toxicity.  Included in this study was a negative control (chamber exposed) group and a positive control group that was treated via gastric intubation on gestational days 6-15 with 400mg/kg/day of acetylsalicylic acid.  All surviving females were sacrificed on Day 21 of testation and fetuses examined for external, soft tissue and skeletal malformations.  Pregnancy rate, mortality, body weight gain and gross postmortem observations were unaffected by treatment.  MRD-77-44 treatment at either dose level had no effect on reproductive endpoints, fetal size, sex distribution, ossification variation, or fetal examination endpoints.    Thus, there was no evidence of maternal or fetal toxicity at either exposure level of MRD-77-44 tested.  Based on these results, both the maternal and developmental NOAELs were greater than or equal to 900 ppm (5220 mg/m^3).