title: Bioassay of tolazamide for possible carcinogenicity.
abstract: A bioassay of the hypoglycemic drug tolazamide for possible carcinogenicity was conducted by administering the test chemical in feed to Fischer 344 rats and B6C3F1 mice. Groups of 35 rats and 35 mice of each sex were administered tolazamide at one of two doses, either 5,000 or 10,000 ppm, for 103 weeks. Matched controls consisted of 15 rats and 15 mice of each sex. All surviving rats and mice were killed at 104 or 105 weeks. Survival rates for the dosed rats of each sex were higher than those for the matched controls, and were adequate for the development of late-appearing tumors. Survival rates for the mice were lower than those for the rats, particularly for the dosed females (matched controls 67%, low-dose 34%, high-dose 32%). However, a large number of these deaths in the dosed females occurred after 90 weeks on study, and survival of both males and females was adequate for the development of late-appearing tumors. All observed tumors were of types commonly found in the strains of animals used, and there were no statistically significant increases in the incidence of tumors in the dosed animals as compared with controls. It is concluded that under the conditions of this bioassay, tolazamide was not carcinogenic for Fischer 344 rats or B6C3F1 mice.