Used primarily in research settings as a selective inhibitor of the cytochrome P450 enzyme CYP2C9, Sulfaphenazole helps in studying drug metabolism and enzyme kinetics. It is employed in vitro to assess the role of CYP2C9 in the biotransformation of various drugs, especially those metabolized in the liver. Due to its inhibitory action, it aids in identifying potential drug-drug interactions involving CYP2C9 substrates such as warfarin, phenytoin, and nonsteroidal anti-inflammatory drugs. It is not used clinically as a therapeutic agent but remains a valuable tool in pharmacological and toxicological research.