Astemizole-d3 is primarily used in research and analytical applications as an internal standard in mass spectrometry studies. It helps in the accurate quantification and detection of astemizole and its metabolites in biological samples. This deuterated compound is particularly valuable in pharmacokinetic and pharmacodynamic studies, enabling researchers to trace the behavior of astemizole in the body with high precision. Its use ensures reliable and reproducible results in drug metabolism and toxicology research.