ABSTRACT
This chapter addresses the processes of drug distribution and excretion, as well as gives an introduction to the pharmacokinetic variables involved in the absorption, distribution, and elimination of drugs. After a drug is absorbed into the bloodstream, it circulates throughout the body and has the possibility of entering various organs and tissues. Endothelial cells line the inside of the heart, blood vessels, and lymphatic vessels. Capillary permeability to drugs can vary depending on how tight the junctions are between endothelial cells. Binding to plasma proteins can cause a drug to remain largely in the blood compartment. The most common protein involved in this type of interaction is albumin, which comprises about 50% of the total protein in blood. The affinity of a drug for a tissue may be due to several interactions, including binding to tissue proteins, binding to nucleic acids, or dissolution into the lipid material. Often there may be competition between drugs for the binding sites of macromolecules.
