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Administrative data

toxicity to reproduction: other studies
Type of information:
migrated information: read-across based on grouping of substances (category approach)
Adequacy of study:
supporting study
Study period:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Well documented publication which meets basic scientific principles and provides strong evidence to support the mode of action for the hypothesis that developmental effects seen in developmental toxicity studies are secondary to maternal toxicity.

Data source

Reference Type:
Diflunisal-induced maternal anemia as a cause of teratogenicity in rabbits
Clark, R.L., Robertson, R.T., Minsker, D.H., Cohen, S.M., Tocco, D.J., Allen, H.L., James, M.L., and Bokelman, D.L.
Bibliographic source:
Teratology 30, 319-332.

Materials and methods

Test guideline
no guideline followed
Principles of method if other than guideline:
The study followed the basic principles of a developmental toxicity study but used a single dose on GD 5. This was designed to produce an anaemia that would be much more persistent than the drug itself, which is cleared quite rapidly from the animals' system. The study is therefore designed to see if hypoxia is the secondary cause of the developmental toxicity seen with the drug rather than it being a direct acting developmental toxicant.
GLP compliance:
not specified
Type of method:
in vivo

Test material

Details on test material:
Source: Merck Sharp & Dohme Research Laboratories, West Point, PA
Molecular Formula C13H8F2O3
Molecular Weight 250.20
CAS Registry Number 22494-42-4
EINECS 245-034-9

Test animals

New Zealand White
Details on test animals and environmental conditions:
- Source: Charles River, WIlmington MA

Administration / exposure

Route of administration:
oral: unspecified
not specified
Details on exposure:
To test the possible causality between the teratogenic effects and anemia induced by diflunisal, a single dose of 180 mg/kg diflunisal was administered to rabbits on gestation day 5.
Analytical verification of doses or concentrations:
not specified
Frequency of treatment:
Single dose on GD 5.
Duration of test:
to GD 20
Doses / concentrations
Doses / Concentrations:
actual ingested
No. of animals per sex per dose:
Control animals:
Details on study design:
To test the possible causality between the teratogenic effects and anemia induced by diflunisal, a single dose of 180 mg/kg diflunisal was administered to rabbits on gestation day 5. This treatment produced an anemia that persisted through gestation day 15 in addition to causing the characteristic axial skeletal defects. Since diflunisal was cleared from maternal blood before gestation day 9, the critical day for induction of similar axial skeletal defects by hypoxia, the skeletal malformations probably resulted from maternal hypoxia secondary to anemia and not from a direct and specific effect of the drug on the embryo.

Results and discussion

Effect levels

Dose descriptor:
Effect level:
< 180 mg/kg bw/day (nominal)
Based on:
test mat.
Basis for effect level:
other: Qualitative nature of result and mode of action are more important than actual NOAEC.

Observed effects

Pregnant does given a single oral dose of diflunisal on gd 5 exhibited anemia that persisted through to gd 15, despite clearance of the drug from maternal blood by gd 9. Signs of anemia (present within 16 hours of dosing) in pregnant does included hemoglobinuria, and decreased erythrocyte counts (a 74 to 46 % decrease relative to controls on gd 9 to 15) and decreased hemoglobin concentrations (a 63 to 21 % decrease relative to controls on gd 9 to 15). Hematotoxicity was the most severe on gd 9, the first day of data collection, with some recovery by gd 15. These does showed an increase in preimplantation loss (10 of 25 inseminated does showed no evidence of implantations and there was an increase in preimplantation loss in other does), as well as an increase in totally resorbed litters (11 of 25 litters).

Any other information on results incl. tables

Effects were attributed to maternal anemia rather than a direct effect of diflunisal, because diflunisal is highly protein bound in maternal blood (greater than 98 %); thus, there are only low concentrations of diflunisal in rabbit embryos. Furthermore, rats, which are resistant to diflunisal-induced maternal anemia, do not demonstrate embryo/fetal effects, despite reaching approximately equivalent doses of diflunisal in rat embryos. Furthermore, there is little accumulation of diflunisal in embryos, which is likely a reflection of its low placental transfer. This study provides strong evidence that the embryo/fetal effects (similar to those seen with 2-(2-(2-butoxyethoxy)ethoxy)ethanol) were secondary to maternal anemia.

Applicant's summary and conclusion

Anaemina causes embrotoxicity and fetal toxicity. The results provide strong support to the hypothesis that similar effects seen in studies with 2-(2-(2-butoxyethoxy)ethoxy)ethanol are secondary to anaemia
Executive summary:

In a developmental toxicity study designed to establish the mechanism of toxicity of the anti-inflammatory drug, diflunisal, pregnant rabbits were given a single 100mg/kg dose of the drug on GD5. The known metabolism of the drug meant that it would be cleared from the bloodstream by GD9, which is known to be the critical day for the induction of axial skeletal defects by hypoxia. Diflunisal also causes anaemia, which is persistent to GD15 and the study produced the same axial skeletal defects that were seen in a conventional developmental toxicity study. The results provided strong support for the hypothesis that, for this drug, the developmental toxicity was primarily caused by anaemia rather than directly by the drug itself.