Axitinib-d3, a deuterated form of axitinib, is primarily used in research and development as an internal standard in mass spectrometry-based assays. Its application is crucial for the accurate quantification of axitinib in biological samples, such as plasma or serum, during pharmacokinetic studies. The deuterium labeling provides a distinct mass difference, enabling precise detection and measurement without interference from the non-deuterated compound. This is particularly valuable in drug development and clinical trials, where understanding the drug's absorption, distribution, metabolism, and excretion is essential. Additionally, Axitinib-d3 aids in ensuring the reliability and reproducibility of analytical methods, supporting the development of therapeutic strategies involving axitinib.