Bioassay of phthalamide for possible carcinogenicity.
A bioassay of phthalamide for possible carcinogenicity was conducted by administering the test chemical in feed to F344 rats and B6C3F1 mice. Groups of 50 rats of each sex were administered phthalamide at one of two doses, either 15,000 or 30,000 ppm for the males and either 5,000 or 10,000 ppm for the females, for 106 weeks. Groups of 50 mice of each sex were administered the test chemical at one of two doses, 25,000 or 50,000 ppm for the males, and at one of three doses, 6,200, 12,500, or 25,000 ppm, for the females, for 103 or 105 weeks. Matched controls consisted of 20 untreated rats of each sex, 20 untreated male mice, and two groups of 20 untreated female mice. All surviving rats and mice were killed at the end of administration of the test chemical. Mean body weights of the dosed groups of rats and mice were either slightly lower than those of corresponding control groups or essentially unaffected by administration of the test chemical. Also, survival was unaffected in the rats and mice except for early deaths in the high- and mid-dose groups of female mice. Survival was 66% or greater at the end of the bioassay in all dosed groups and control groups of each species and sex except for the high-dose group of female mice (36%). With the exception of the high-dose female mice, sufficient numbers of animals were at risk in all groups for the development of late-appearing tumors. No tumors occurred in the rats or mice of either sex at incidences that were significantly higher in the dosed groups than in the corresponding control groups. However, phthalamide produced toxic lesions in the livers of male and female rats and the urinary systems of female rats and mice. The presence of nonneoplastic lesions suggests that the MTD may have been used or exceeded. It is concluded that under the conditions of this bioassay, phthalamide was not carcinogenic for F344 rats or B6C3F1 mice of either sex.