Anileridine-d4 is primarily used in research and analytical settings as a labeled internal standard for the quantification of anileridine in biological samples. It is particularly valuable in mass spectrometry-based assays, where its deuterium atoms provide a distinct mass signature, enabling precise and accurate measurement of anileridine levels in complex matrices like blood, urine, or plasma. This application is critical in pharmacokinetic studies, forensic toxicology, and drug metabolism research, where understanding the distribution, absorption, and elimination of anileridine is essential. Additionally, it aids in ensuring the reliability and reproducibility of analytical methods by minimizing variability in sample preparation and analysis.