Etofenamate-d4 is primarily used as an internal standard in analytical chemistry for the quantification of etofenamate in various samples. Its deuterated structure ensures it behaves similarly to etofenamate during analysis, allowing for precise and accurate measurements in techniques like liquid chromatography-mass spectrometry (LC-MS). This application is crucial in pharmaceutical research and quality control, where determining the concentration of etofenamate in formulations or biological samples is essential. Additionally, it aids in pharmacokinetic studies to understand the absorption, distribution, metabolism, and excretion of etofenamate in the body.