Zileuton-d4 is primarily used in research and development as an internal standard in analytical chemistry. It is employed in mass spectrometry and chromatography techniques to ensure accurate quantification of zileuton, a drug used to treat asthma. The deuterated form helps in distinguishing the analyte from the internal standard, improving precision and reliability in pharmacokinetic studies and drug metabolism research. Its application is crucial in understanding the absorption, distribution, metabolism, and excretion of zileuton in biological systems.