ADME studies are used to look at how drugs are processed by the body. Essentially, they measure how a drug makes its way throughout the body, how the drug is metabolized or inactivated, and how the body gets rid of the active and inactive metabolites.
A powerful way to measure this is through the use of radiolabeled compounds. By adding a radioactive isotope such as tritium or carbon-14 to a drug candidate, it is possible to accurately measure the amount of compound within plasma, urine, feces, and bile. ADME studies are not just important in drug development; they are required because they directly relate to human safety evaluations. By looking at exposures in testing species and comparing metabolites in animals and humans, it becomes possible to validate the choice of species for toxicology studies.
One important consideration in radiolabeled studies is the use of isotope. The radiolabeling process can be intensive depending on the choice of isotope. For instance, it is frequently easier to label compounds with tritium than C-14 because hydrogen atoms are more accessible for replacement, whereas substituting a carbon atom within a coumpound can require more complex chemistry. Additionally, the location of the radiolabeling is important - if the label is on a part of the compound that is cleaved off during first pass metabolism, recovery of radiolabeled compound can be altered.
These are just a few considerations when constructing a radiolabeled ADME program. If you are in the process of constructing an ADME program, PBL may be able to assist you with more information about our radiolabeled ADME testing services.