Methapyrilene is inactive in the hepatocyte-mediated Chinese hamster ovary/hypoxanthine-guanine phosphoribosyl transferase mutational assay.

Methapyrilene, tested at both non-hepatocytotoxic and hepatocytotoxic concentrations, failed to induce somatic mutations in the hepatocyte-mediated Chinese hamster ovary/hypoxanthine-guanine phosphoribosyl transferase (HGPRT) mutational assay. These data support the conclusion that methapyrilene induces the carcinogenesis process through a non-DNA damaging mechanism, suggested when this antihistamine previously failed to induce a genotoxic response in several in vitro test systems developed to detect carcinogens and mutagens.