Used in research settings as a stable isotope-labeled internal standard for the quantification of adefovir in biological samples through mass spectrometry. This labeled analog helps ensure accurate measurement of drug concentrations in pharmacokinetic and metabolic studies. It is particularly valuable in tracing the distribution and elimination of adefovir in vivo without altering the chemical behavior of the compound. Commonly applied in drug development and therapeutic drug monitoring to support antiviral therapy research, especially for hepatitis B virus.