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In pharmacology, clearance ) is a pharmacokinetic ... liver, lungs, etc. Thus, total body clearance is equal to the sum clearance of the substance by each organ (e.g ...
The liver is the major site of first pass effect; however, it can also occur in the lungs, vasculature or other metabolically active tissues in the body. Notable drugs that experience a significant first pass effect are buprenorphine , chlorpromazine , cimetidine , diazepam , ethanol (drinking alcohol), imipramine , insulin , lidocaine ...
Clearance is therefore expressed as the plasma volume totally free of the drug per unit of time, and it is measured in units of volume per units of time. Clearance can be determined on an overall, organism level («systemic clearance») or at an organ level (hepatic clearance, renal clearance etc.). The equation that describes this concept is:
The "Hepatic Extraction Ratio" is a similar measurement for clearance of a substance (usually a pharmacological drug) by the liver. It is defined as the fraction of drug removed from blood by the liver, and depends on 3 factors— the hepatic blood flow, the uptake into the hepatocytes, and the enzyme metabolic capacity.
Enterohepatic circulation of drugs. Enterohepatic circulation is the circulation of biliary acids, bilirubin, drugs or other substances from the liver to the bile, followed by entry into the small intestine, absorption by the enterocyte and transport back to the liver.
Typically, the biological half-life refers to the body's natural detoxification (cleansing) through liver metabolism and through the excretion of the measured substance through the kidneys and intestines. This concept is used when the rate of removal is roughly exponential. [6]
In pharmacology, the area under the plot of plasma concentration of a drug versus time after dosage (called “area under the curve” or AUC) gives insight into the extent of exposure to a drug and its clearance rate from the body. [2]
Volume of distribution may be increased by kidney failure (due to fluid retention) and liver failure (due to altered body fluid and plasma protein binding). Conversely it may be decreased in dehydration. The initial volume of distribution describes blood concentrations prior to attaining the apparent volume of distribution and uses the same ...