Modeling the time dependent biodistribution of Samarium-153 ethylenediamine tetramethylene phosphonate using compartmental analysis

Aim

The main purpose of this work was to develop a pharmacokinetic model for the bone pain palliation agent Samarium-153 ethylenediamine tetramethylene phosphonate (¹⁵³Sm]-EDTMP) in normal rats to analyze the behavior of the complex.

Background

The use of compartmental analysis allows a mathematical separation of tissues and organs to determine the concentration of activity in each fraction of interest. Biodistribution studies are expensive and difficult to carry out in humans, but such data can be obtained easily in rodents.

Materials and methods

We have developed a physiologically based pharmacokinetic model for scaling up activity concentration in each organ versus time. The mathematical model uses physiological parameters including organ volumes, blood flow rates, and vascular permabilities; the compartments (organs) are connected anatomically. This allows the use of scale-up techniques to predict new complex distribution in humans in each organ.

Results

The concentration of the radiopharmaceutical in various organs was measured at different times. The temporal behavior of biodistribution of ¹⁵³Sm-EDTMP was modeled and drawn as a function of time.

Conclusions

The variation of pharmaceutical concentration in all organs is described with summation of 6–10 exponential terms and it approximates our experimental data with precision better than 2%.