ABSTRACT
The rapid growth of knowledge in the field of drug metabolism and disposition reflects to a large extent the utilization of radioactive isotopes as tracers of chemical and biological processes. The use of total radioactivity measurements allows an estimation of the total exposure to drug-related material and facilitates the achievement of material balance. During the synthesis of radiolabeled compounds, the label is usually introduced as part of the molecular skeleton and specifically into a metabolically stable and, in the case of tritium, nonexchangeable position. The desired specific activity of the administered radioactive compound depends on the dose to be used as well as the species studied. A logical approach is to use minimal radioactivity that allows the description of the time course of the labeled substance in the animal for a sufficient period of time. In radioactivity measurements, the sample count rate is obtained by subtracting a background from the gross count rate.
