Avosentan-d3 is primarily utilized in research and development within the pharmaceutical industry. It serves as a stable isotope-labeled internal standard in mass spectrometry-based assays, enabling precise quantification of avosentan and its metabolites in biological samples. This application is critical for pharmacokinetic studies, drug metabolism research, and bioanalytical method validation. By providing accurate and reliable measurements, it aids in understanding the drug's behavior in the body, optimizing dosing regimens, and ensuring safety and efficacy in clinical trials. Its use is limited to laboratory settings and is not intended for therapeutic or diagnostic purposes.