Extraction ratio

Extraction ratio is a term used in pharmacology to describe the proportion of a drug that is removed from the body during its passage through an organ in the body. It is a measure of the efficiency of the organ in extracting the drug from the blood.

Definition

The extraction ratio (E) of a drug is defined as the fraction of the drug that is removed from the body during its passage through an organ. It is calculated using the formula:

E = (C_in - C_out) / C_in

where C_in is the concentration of the drug in the blood entering the organ, and C_out is the concentration of the drug in the blood leaving the organ.

Factors affecting extraction ratio

The extraction ratio of a drug can be affected by several factors, including:

• The blood flow to the organ: A higher blood flow can increase the extraction ratio, as it allows more of the drug to be exposed to the organ.
• The binding affinity of the drug for the organ: A higher binding affinity can increase the extraction ratio, as it allows more of the drug to be taken up by the organ.
• The metabolic capacity of the organ: A higher metabolic capacity can increase the extraction ratio, as it allows more of the drug to be metabolized and removed from the body.

Clinical significance

The extraction ratio of a drug can have important implications for its pharmacokinetics and pharmacodynamics. For example, drugs with a high extraction ratio are typically cleared from the body more quickly, which can affect their therapeutic effect and side effect profile.

See also

• Clearance (pharmacology)
• Volume of distribution
• Bioavailability
• Half-life (pharmacology)