ABSTRACT

This chapter focuses on the compartmental models to illustrate the kinetics of active and passive transport. A passive transport process can often be described by a first-order equation. Passive transport may be characterized by the following: drug molecules move from a region of relatively high concentration to one of lower concentration and the rate of transfer is proportional to the concentration gradient between the compartments involved in the transfer. The change in drug concentration between regions as a function of time involves rate processes which may or may not include the participation of body enzymes. When a fruitful collision occurs between drug and carrier, then the transport of drug across the membrane as a drug-carrier complex occurs in the normal manner. The kinetic order can change to apparent zero order when drug concentration is increased from dilute conditions to those of capacity-limited transfer.