ABSTRACT
Radiolabeled drugs are used in drug metabolism studies to detect any drug metabolites that are formed. In order to study drug metabolism, it is necessary to incorporate an identifiable isotope into the drug. There are several advantages in using carbon isotopes for drug metabolism studies, rather than deuterium or tritium. However, it is known that N-methyl groups are susceptible to drug metabolism. The isotopes that are commonly used for labeling studies are heavy isotopes such as deuterium and carbon-13, and radioactive isotopes such as tritium and carbon-14. Carbon isotopes are less likely to be lost from a molecule, but it is important to choose positions for the label which are metabolically stable. There are various methods by which deuterium (D) or tritium (T) can be incorporated into a drug. The easiest method is to identify an exchangeable proton in the drug structure and to replace it with D or T.
