Used primarily as a stable isotope-labeled internal standard in analytical chemistry, particularly in mass spectrometry and liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods. It aids in the accurate quantification of fenbendazole and its metabolites in biological samples such as plasma, urine, and tissue. This deuterated analog ensures high precision in pharmacokinetic and metabolic studies due to its nearly identical chemical behavior to non-labeled fenbendazole while being distinguishable by mass detection. Commonly applied in veterinary drug residue monitoring and research on anthelmintic drug distribution and metabolism.