Sulfisoxazole is an antimicrobial drug that is a derivative of sulfanilamide. Although the use of sulfonamide drugs has declined in the past few years due to the emergence of drug-resistant strains of bacteria and the development of newer antimicrobial drugs with fewer side effects, these compounds are still widely prescribed on a chronic basis for the treatment of recurrent urinary tract infections and certain other infectious diseases.
A bioassay of sulfisoxazole for possible carcinogenicity was conducted by administering the chemical by gavage to Fischer 344 rats and B6C3F1 mice.
Groups of 50 rats of each sex and 50 mice of each sex were administered sulfisoxazole suspended in aqueous 0.5% carboxymethyl cellulose 7 days per week at one of two doses, either 100 or 400 mg/kg body weight for the rats and either 500 or 2,000 mg/kg for the mice. Vehicle controls consisted of groups of 50 rats of each sex and 50 mice of each sex that were administered only the aqueous 0.5% carboxymethyl cellulose. Untreated controls consisted of groups of 50 rats of each sex and 50 mice of each sex. The dosed groups of the rats and mice were administered the chemical by gavage for 103 weeks, then observed for 1 to 3 additional weeks; the vehicle-control groups were similarly administered 0.5% carboxymethyl cellulose alone. All surviving rats and mice were killed at weeks 104 to 106.
Mean body weights of high-dose male rats and female mice were slightly lower than those of corresponding vehicle controls during the last 40 to 50 weeks of the bioassay; mean body weights of dosed female rats and male mice were unaffected. Survival rates were unaffected by the test chemical, and adequate numbers of animals were at risk for the development of late-appearing tumors.
No tumors occurred in the dosed groups of rats or mice of either sex at incidences that were significantly higher than those of the vehicle-control groups.
It is concluded that under the conditions of this bioassay, sulfisoxazole was not carcinogenic for either Fischer 344 rats or B6C3F1 mice.