Potentially mutagenic impurities: Analysis of structural classes and carcinogenic potencies of chemical intermediates in pharmaceutical syntheses supports alternative methods to the default TTC for calculating safe levels of impurities

•The TTC was designed to protect from uncharacterized chemicals.•The TTC is a dose so low that the risk of cancer is negligible even for potent mutagenic carcinogens.•Many chemicals in pharmaceutical syntheses are not in structural classes of potent carcinogens.•Chemical class-specific acceptable intakes can be used that maintain negligible risk.•This experience is helpful in developing ICH guideline for mutagenic impurities.