Albendazole sulfoxide D3 is primarily used as an internal standard in analytical chemistry for the quantification of albendazole and its metabolites in biological samples. It plays a critical role in ensuring accuracy and precision in liquid chromatography-mass spectrometry (LC-MS) methods, particularly in pharmacokinetic studies and drug monitoring. This compound is essential for researchers and clinicians to determine drug concentrations in plasma, urine, or tissues, aiding in the optimization of dosing regimens and therapeutic efficacy. Additionally, it supports the development and validation of analytical methods for studying drug metabolism and pharmacokinetics in both preclinical and clinical settings. Its use is particularly significant in veterinary and human medicine for the treatment and monitoring of parasitic infections.