Used as an internal standard in analytical chemistry for the quantification of althiazide in biological samples. Its deuterated form ensures accurate and reliable measurements in mass spectrometry, minimizing interference from non-deuterated althiazide. This application is crucial in pharmacokinetic studies, helping researchers understand the drug's absorption, distribution, metabolism, and excretion in the body. Additionally, it supports the development and validation of analytical methods for therapeutic drug monitoring and clinical research.