Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The plateau principle is a mathematical model or scientific law originally developed to explain the time course of drug action. The principle has wide applicability in pharmacology, physiology, nutrition, biochemistry and system dynamics. It applies whenever a drug or nutrient is infused or ingested at a relatively constant rate and when a constant fraction is eliminated during each time interval. Under these conditions, any change in the rate of infusion leads to an exponential increase or decrease until a new level is achieved. This behavior is also called an approach to steady state because rather than causing an indefinite increase or decrease, a natural balance is achieved when the rate of infusion or production is balanced by the rate of loss.