Mefenamic Acid-d3 is primarily used in research and analytical laboratories as an internal standard for the quantification of mefenamic acid in various biological samples. Its deuterated form ensures accurate and precise measurements in mass spectrometry, minimizing interference from other compounds. This application is crucial in pharmacokinetic studies, where understanding the absorption, distribution, metabolism, and excretion of mefenamic acid is essential. Additionally, it aids in clinical studies to monitor drug levels in patients, ensuring therapeutic efficacy and safety. Its use extends to forensic toxicology, where it helps detect and quantify mefenamic acid in cases of overdose or poisoning.