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Assessment 1.2

Drug Biotransformation

ADME Absorption Distribution Metabolism-what we are covering in these notes Excretion
Biotransformation Metabolism
xenobiotics compounds foreign to the body such as drugs
Enzymes are what carry out biotransformation
Two ways drugs are eliminated from the body through liver and intestine
excreted in urine and feces, which they don't change their chemical structure
metabolized or biotransformed and then excreted, which the chemical structure is changed
The major objective of drug biotransformation reactions in the body is to make nonpolar drugs more polar so that they may be more readily excreted!
Biotransformation results in not only making a drug more soluble for excretion but also often produces a metabolite that is no longer capable of producing a therapeutic response. metabolite-derivative of structure
Biotransformation occurs primarily in the liver,secondary is the gastrointestinal tract, and the last is in the skin and lungs. goal of the liver is make it more polar and excrete, the liver doesn't know how to make it more less active
1st Pass biotransformation in the GI tract adds to that percentage even more such that the amount of an orally ingested drug actually reaching the systemic circulation is significantly reduced.
occurs in the intestine prior to absorption, the bulk of 1st pass metabolism happens in the liver after absorption
Anything in the GI tract is considered to "outside of body", it has to be absorbed to be considered "inside the body"
Portal Vein takes the material to the liver.
Look at page 4 of notes
Cytochrome P450 Enzyme, it catalyzes (changes in the structure of the drug)
cyto-cell chrome-color
isozymes-enzymes with different structures
Cytochrome P450 & Drug Interactions two types: induction and inhibition
Inhibition competitive binding at an enzymes binding site(s), high affinity for an enzymes will slow the metabolism of any low affinity drug at that particular enzyme
Ex: 2 enzymes going to the liver competing for a CYP3A4, one enzyme will occupy the CYP3A4, other enzyme will want it (competitive inhibition) but won't get it, less enzymes and metabolism result will give more drug to body
Induction substance(a drug) stimulates the synthesis of the enzyme or reduce its degradation and the metabolic capacity of that isozyme is increased
more enzyme and metabolism result in less drug body
****** Always the number of enzymes is important, more or less drug*********
Metabolism- absorption of drugm then excretes, not leaving it in the plasma
Inducers-increase amount of enzymes and metabolism, less drug in plasma
Inhibitors- drcrease amount of enzymes and metabolism, more drug in plasma
Prodrugs an inactive compound that is administered and then transformed into an active substance by either chemical or metabolic means
activated in various places- stomach, intestines, liver, blood, and inside cells activated in various ways- cleavage of groups, biotransformation, addition of phosphates.
Examples- Sulindac inactive form taken then becomes active (Sulfide) in the liver. Want to have inactive form until liver because the active form (sulfide) irritates the GI tract.
Biotransformation Reactions Phase I and Phase II- Does NOT have to occur in this order
Phase I- look at page 13 of notes to distinguish reactions functionalization reaction (adding OH, oxidizing a C, hoping to make more polar) loss of activity
make a compound more hydrophilic by introducing or exposing a polar functional group
Phase II- look at page 15 of notes to distinguish reactions biosynthesis reaction (stick something on it) covalent linkage between a functional group and a highly polar conjugate
make a compound more hydrophilic by covalently linking them to a polar compound
Enterohepatic recirculation entero-intestine hepatic-liver higher molecular weight conjugates formed w/ glucuronic acid are excreted in the bile& as a result, are subject to enzymatic cleavage by intestinal microflorea (bugs). This enzymatic cleavage leadas to the release&reabsorption of the parent compound
blood streatm to liver(inside) to intestine(outside of body) via bile duct- to excretion but bugs remove glucoronic and parent structure goes back into the intestine, then circulation
Gluthathione(GSH) tripeptide, found in most tissues (kidney and liver), unusual side chain of gamma
detoxificationof xenobiotics- conjugates on the way of the thiol group to make something that is active, less active
APAP Metabolism- look at page 18 of notes at high levels tylenol is toxic to the liver
higher levels of NAPQI (reacts with free electrons which is very dangerous in the body), this can deplete cellular stores of gluthathione
Created by: lisagoette