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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 ...
Enterohepatic circulation of drugs describes the process by which drugs are conjugated to glucuronic acid in the liver, excreted into bile, metabolized back into the free drug by intestinal bacteria, and the drug is then reabsorbed into plasma.
Pharmacologists have linked drugs to glucuronic acid to allow for more effective delivery of a broad range of potential therapeutics. Sometimes toxic substances are also less toxic after glucuronidation. The conjugation of xenobiotic molecules with hydrophilic molecular species such as glucuronic acid is known as phase II metabolism.
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.
The drug is easily distributed in highly perfused organs such as the liver, heart and kidney. It is distributed in small quantities through less perfused tissues like muscle, fat and peripheral organs. The drug can be moved from the plasma to the tissue until the equilibrium is established (for unbound drug present in plasma).
Ethanol is highly water-soluble and diffuses passively throughout the entire body, including the brain. Soon after ingestion, it begins to be metabolized, 90% or more by the liver. One standard drink is sufficient to almost completely saturate the liver's capacity to metabolize alcohol.
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