International Agency for Research on Cancer (IARC) - Summaries & Evaluations

(Group 3)

For definition of Groups, see Preamble Evaluation.

Vol.: 79 (2001) (p. 361)

CAS No.: 723-46-6
Chem. Abstr. Name: 4-Amino-N-(5-methyl-3-isoxazolyl)benzenesulfonamide

5.  Summary of Data Reported and Evaluation

5.1 Exposure data

Sulfamethoxazole is a sulfonamide drug. It is used worldwide in the treatment of bacterial and protozoal infections, particularly in combination with other drugs in treating acute urinary tract infections and malaria.

5.2 Human carcinogenicity data

In one hypothesis-seeking epidemiological study, statistically significant positive associations were noted between sulfamethoxazole use and the risks for cancers of the lung and cervix and multiple myeloma and the combination of lymphomas and leukaemias.

5.3 Animal carcinogenicity data

Sulfamethoxazole was tested by oral administration in one study in rats. It produced follicular-cell adenomas and carcinomas of the thyroid.

5.4 Other relevant data

Sulfamethoxazole does not appear to be polymorphically acetylated in humans. Sulfamethoxazole is metabolized to its potentially toxic hydroxylamine in both humans and experimental animals. This metabolite has been associated with idiosyncratic toxicity, such as systemic hypersensitivity reactions, in humans. Sulfamethoxazole induced thyroid enlargement and hyperplasia in rats but not in monkeys. There is no convincing evidence that sulfamethoxazole alters thyroid hormone homeostasis in rats.

Administration of sulfamethoxazole to patients at therapeutic doses in combination with trimethoprim increased the number of micronuclei in their bone-marrow cells but did not increase the frequency of chromosomal aberrations. Sulfamethoxazole did not induce chromosomal aberrations in human lymphocytes in vitro or mutations in bacteria. Insufficient data were available to reach a conclusion about the genotoxicity of the agent.

5.5 Evaluation

There is inadequate evidence in humans for the carcinogenicity of sulfamethoxazole.

There is limited evidence in experimental animals for the carcinogenicity of sulfamethoxazole.

Overall evaluation

Sulfamethoxazole is not classifiable as to its carcinogenicity to humans (Group 3).

For definition of the italicized terms, see Preamble Evaluation.

Previous evaluations: Vol. 24 (1980); Suppl. 7 (1987)


Last updated: 25 September 2001

    See Also:
       Toxicological Abbreviations
       Sulfamethoxazole  (IARC Summary & Evaluation, Supplement7, 1987)
       Sulfamethoxazole  (IARC Summary & Evaluation, Volume 24, 1980)