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PharmD clinical pharmacy program Level 3, Semester 2 Biopharmaceutics & Pharmacokinetics (PT608(

Clearance

Drug clearance (also called body clearance or total body clearance, and abbreviated

as Cl or Cl T)

It is a proportionality constant describing the relationship between a substance’s rate

of elimination (amount per unit time) at a given time and its corresponding concentration

in an appropriate fluid at that time.

Clearance can also be defined as ‘‘the hypothetical volume of blood (plasma or

serum) or other biological fluids from which the drug is totally and irreversibly removed

per unit time.

The larger the hypothetical value, the more efficient is the eliminating organ (kidney

and liver). One limiting factor is the volume of the blood that is presented to the

eliminating organ per unit time.

➢ For kidney, the upper limit of blood flow is 19 mL min kg
-1
-1
➢ For liver, the upper limit of blood flow is approximately 1.5 L min
-1
Another limiting factor is the extraction ratio of the organ for the drug being

eliminated.

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