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First-pass metabolism may occur in the liver (for propranolol, lidocaine, clomethiazole, and nitroglycerin) or in the gut (for benzylpenicillin and insulin). [4] The four primary systems that affect the first pass effect of a drug are the enzymes of the gastrointestinal lumen, [5] gastrointestinal wall enzymes, [6] [7] [8] bacterial enzymes [5] and hepatic enzymes.
Drug metabolism is the metabolic breakdown of drugs by living organisms, usually through specialized enzymatic systems. More generally, xenobiotic metabolism (from the Greek xenos "stranger" and biotic "related to living beings") is the set of metabolic pathways that modify the chemical structure of xenobiotics, which are compounds foreign to an organism's normal biochemistry, such as any drug ...
Many drugs that are absorbed through the GI tract are substantially metabolized by the liver before reaching general circulation. This is known as the first pass effect . As a consequence, certain drugs can only be taken via certain routes.
For example, antibiotics that kill gut bacteria often reduce enterohepatic drug circulation and this requires a temporary increase of the drug's dose until the antibiotic use is discontinued and the gut repopulates with bacteria. This effect of antibiotics on enterohepatic circulation of other drugs is one of several types of drug interactions.
Glucuronidation is often involved in drug metabolism of substances such as drugs, pollutants, bilirubin, androgens, estrogens, mineralocorticoids, glucocorticoids, fatty acid derivatives, retinoids, and bile acids. These linkages involve glycosidic bonds. [1]
Albumin, carries thyroid hormones and other hormones, particularly fat soluble ones, fatty acids to the liver, unconjugated bilirubin, many drugs and Ca 2+ Ceruloplasmin, carries copper; Transcortin, carries cortisol, aldosterone and progesterone; Haptoglobin, carries free hemoglobin released from erythrocytes
Food such as fructose can increase the rate of alcohol metabolism. The effect can vary significantly from person to person, but a 100 g dose of fructose has been shown to increase alcohol metabolism by an average of 80%. In people with proteinuria and hematuria, fructose can cause falsely high BAC readings, due to kidney-liver metabolism. [106]
Compounds begin to break down as soon as they enter the body. The majority of small-molecule drug metabolism is carried out in the liver by redox enzymes, termed cytochrome P450 enzymes. As metabolism occurs, the initial (parent) compound is converted to new compounds called metabolites. When metabolites are pharmacologically inert, metabolism ...