Itraconazole-d5 is primarily used as an internal standard in analytical chemistry for the quantification of itraconazole in various biological samples. Its deuterated form ensures accurate and precise measurements in mass spectrometry, minimizing interference from the non-deuterated compound. This application is crucial in pharmacokinetic studies, therapeutic drug monitoring, and research on drug metabolism, where understanding the concentration and behavior of itraconazole in the body is essential. Additionally, it aids in the development and validation of analytical methods, ensuring reliability and reproducibility in clinical and pharmaceutical research.