Used as an internal standard in mass spectrometry and chromatography for the accurate quantification of ranitidine in biological samples such as plasma, serum, and urine. Its deuterated structure allows clear differentiation from non-labeled ranitidine, improving measurement precision in pharmacokinetic and metabolic studies. Commonly applied in drug development, bioavailability testing, and clinical diagnostics where reliable detection and quantification of ranitidine levels are required. Also used in stability-indicating assays to monitor degradation products without interference from endogenous compounds.