Cilazapril-d5 is primarily used in research and development as a stable isotope-labeled internal standard in analytical chemistry. Its application is crucial in quantitative mass spectrometry, where it aids in the accurate measurement of cilazapril and its metabolites in biological samples. By providing a reference point, it enhances the precision and reliability of pharmacokinetic and pharmacodynamic studies. This compound is particularly valuable in clinical trials and drug monitoring, ensuring consistent and reproducible results in the analysis of cilazapril's behavior in the body. Its use supports the development of new therapeutic strategies and the optimization of existing treatments for hypertension and heart failure.