Effect of drug transit time between exchange locus with plasma and sampling site

In pharmacokinetic models used to describe the behavior of drugs in living organisms, generally neither the amount of drug flowing in pipes between compartments nor the transfer delay between the plasma-lymph exchange areas and a site of measurement are taken into account. Several former publications dealt with exchanges between two or more different organs assuming that the blood flow was constant or that the variation of the lymphatic flow was negligible or noting that the amount of drug present in pipes was not easily taken into account. In this article, we deal with concentration in a site of interstitial exchanges with regard to concentration in a sampling site with a varying blood flow, assuming that the transit time depends both on the fluid flow and the path length through pipes. In all considered cases, the plasma concentration profile may be highly altered by a change in the flow rate.