Clearance (pharmacology)

Clearance (pharmacology)

Clearance in the context of pharmacology refers to the rate at which a particular substance is removed from the body, typically through the kidneys. It is a key concept in the field of pharmacokinetics, the study of how the body processes drugs. Pronounced as /ˈklɪərəns/.

Etymology

The term "clearance" comes from the English word "clear", which in this context means to remove or eliminate. The term was first used in pharmacology in the early 20th century.

Definition

In pharmacology, clearance is a pharmacokinetic parameter that describes the volume of plasma from which a substance is completely removed per unit time. The units of clearance are usually volume/time (e.g., mL/min or L/h). Clearance is not a measure of the amount of drug removed, rather it is a measure of the efficiency of elimination of a drug from the body.

Calculation

Clearance is calculated using the formula:

Clearance = Dose / Area Under the Curve (AUC)

Where:

Dose is the amount of drug administered.
AUC is the area under the plasma concentration-time curve, which represents the total exposure of the body to the drug.

Factors affecting clearance

Several factors can affect the clearance of a drug, including:

Kidney function: The kidneys are the primary organs responsible for drug clearance. Impaired kidney function can reduce drug clearance.
Liver function: The liver also plays a key role in drug metabolism and clearance. Liver disease can reduce drug clearance.
Age: Clearance can be affected by age, with clearance generally decreasing with increasing age.
Body weight: Clearance can be affected by body weight, with larger individuals generally having higher clearance rates.

Related terms

Volume of distribution: This is a measure of how a drug is distributed in the body's tissues.
Half-life: This is the time it takes for the concentration of a drug in the body to decrease by half.
Bioavailability: This is the proportion of a drug that enters the circulation when introduced into the body.