Tutorial for beginners: the concept of clearance explained using the example of a vacuum cleaner

ABSTRACT

Clearance is a key concept in pharmacokinetics, but it is not easy to understand for beginners. This tutorial aims to help beginners by using the analogy of a vacuum cleaner clearing the dust from the air in a room. The air, the volume of the air, the dust and the vacuum cleaner are used to represent the plasma, the volume of distribution, the drug and the eliminating organ, respectively, in the human body. Because the capacity of a vacuum cleaner (eliminating organ) is an inherent feature that is independent of the concentration of dust (drug), the elimination rate (eliminated amount/time) of dust (drug), which is proportional to its concentration in the air (plasma), cannot reflect this inherent capacity correctly. Clearance estimates the volume of the solvent (air or plasma) cleared by the organ per unit time rather than the amount of the solute (dust or drug) removed. Therefore, clearance has the unit of volume/time. Just as the air is cleared of dust, but is not eliminated by the vacuum cleaner, the plasma is cleared of drug, but is not eliminated from the human body.