Clearance (medicine)

Clearance (medicine) is a pharmacological term that refers to the volume of plasma from which a substance is completely removed per unit time. The concept of clearance is used to understand the rate at which drugs are eliminated from the body.

Definition

In pharmacokinetics, clearance is a measurement of the volume of plasma from which a substance is completely removed per unit time. The units of clearance are typically mL/min or L/h. Clearance is a hypothetical volume that is cleared of drug per unit time. The concept of clearance is used to quantify the rate at which a drug is eliminated from the body.

Mechanisms of Clearance

Clearance of a drug can occur through various mechanisms including metabolism, excretion, and distribution into peripheral compartments. The liver and kidneys are the primary organs responsible for the clearance of most drugs.

Metabolism

Metabolism is a major route of drug clearance. The liver is the primary site of drug metabolism. Drugs can be metabolically transformed in the liver to more polar, water-soluble metabolites that can be more readily excreted by the kidneys.

Excretion

Excretion is another major route of drug clearance. The kidneys are the primary organs responsible for the excretion of drugs and their metabolites. Drugs can be excreted in the urine by glomerular filtration, tubular secretion, or both.

Distribution

Distribution into peripheral compartments can also contribute to the clearance of a drug. Some drugs can be sequestered in peripheral tissues, effectively removing them from the systemic circulation and reducing their concentration in the plasma.

Factors Affecting Clearance

Several factors can affect the clearance of a drug, including the drug's physicochemical properties, the individual's physiological state, and the presence of disease.

Physicochemical Properties of the Drug

The physicochemical properties of a drug, such as its lipophilicity, molecular size, and ionization state, can influence its clearance. For example, highly lipophilic drugs are more likely to be metabolized and cleared by the liver, while large or highly charged drugs are more likely to be cleared by the kidneys.

Physiological State

The physiological state of an individual can also affect drug clearance. For example, clearance can be affected by age, sex, body weight, and organ function. In particular, liver and kidney function are critical for drug clearance.

Disease State

Disease states can also affect drug clearance. For example, liver or kidney disease can significantly reduce the clearance of drugs that are primarily cleared by these organs.

See Also

• Pharmacokinetics
• Metabolism
• Excretion
• Distribution (pharmacology)