Used as a stable isotope-labeled internal standard in mass spectrometry-based bioanalytical studies to accurately quantify repaglinide and its metabolites in biological matrices such as plasma, serum, or urine. Its deuterated ethyl group provides a distinct mass difference, enabling clear differentiation from non-labeled compounds during detection. This ensures high specificity and precision in pharmacokinetic and metabolic studies, especially in drug development and clinical research involving antidiabetic agents.