Drug distribution is the reversible transport of a drug from one part of the body to another. • Usually is used to describe the translocation of drug from blood stream to tissue. • Distribution is generally uneven because of differences in blood perfusion, tissue binding (e.g., because of lipid content), regional pH, and permeability of cell membranes. • Steady-state is the term employed when the 

concentration of drug in all parts of the body are constant. 

Distribution Compartments • 1. Central Compartment, includes the well-perfused organs and tissues (heart, blood, liver, brain and kidney) which drug equilibrates rapidly. • 2. Peripheral Compartment(s), include(s) those organs (e.g., adipose and skeletal muscle) which are less well-perfused, and drug therefore equilibrates more slowly. Redistribution from one compartment to another often alters the duration of effect at the target tissue. • 3. Special Compartments, Entry of drug into the cerebrospinal fluid (CSF) and central nervous system (CNS) is restricted by the structure of the capillaries and pericapillary glial cells. Drugs also have relatively poor access to pericardial fluid, bronchial secretions and fluid in the middle ear.