Can you answer these, they have to do with drug metabolism? 3. Explain the first

Question

Can you answer these, they have to do with drug metabolism?

3. Explain the first pass effect of a chemical following oral administration and how this can alter the effective bioavailability of a chemical. (No more than 5 sentences) 5 pts 4. What is the purpose of a phase I reaction? Describe one phase I reaction and how it alters a drug. (No more than 3 sentences) 3 pts 5. How does a Phase Il reaction effect the excretion of an intermediate drug (No more than 2 sentences)? 2 pts 6. Define enzyme induction and enzyme inhibition. Give an example of how enzyme induction alters the pharmacological effect of a drug and give an example of how enzyme inhibition alters the pharmacological effect of a drug (examples can be generalized and not specific drugs) (No more than 4 sentences) 4 pts

Explanation / Answer

3.

a. The first pass effect is a phenomenon of drug metabolism whereby a fraction of drug is lost during absorption leading to reduction in the concentration of the drug that finally reaches the systemic circulation.

b. Most of the first -pass phenomenon occur in the liver or the gut. Bioavailability is the fraction of the administered dose that gets into circulation. Thus, this phenomenon may greatly reduce the bioavailabilty of the drug.

c. The liver at times metabolizes the drugs to such an extent that only a fraction of the active drug gets into the circulation leading to a very reduced bioavailability of the drug. Therefore people with liver cirhosis have a high bioavailability by oral administration.

d. There are 4 primary system that effects the first-pass are the gastrointestinal enzymes, gut wall enzymes, bacterial enzymes, and hepatic enzymes. Hence, most of the drug designing fails in the first-pass mechanism.

4. a. Phase I biotransformation increases the polarity of the drug by introducing or exposing functional groups of the compound. this makes the hydrophic compunds more water-soluble leading to a proper excretion of the compounds.

b. The phase I reactions are broadly grouped into 3 categories: oxidation, reduction and hydrolysis.

c. One reaction of Phase I : Hydrolysis: R-COO-R' + H2O = R-COOH + R'-OH

Example: conversion of cocaine to benzoylecognine which is soluble in water is excreted through urine. this compound is often tested for in cocaine urinalysis.

5. a. In phase II, activated metabolites are conjugated with charged species, which increases the molecular weight of the compound.

b.This phase makes the compound less active. This addition detoxifies the reactive electrophiles and produces polar compounds, which can be eliminated or excreted.

6. a.Enzyme induction means activation of an enzyme by a compound. Enzyme inhibition means inhibition of expression of an enzyme by another molecule.

b. enhancement of drug metabolism due to tobacco smoking may involve enzyme induction.

c.  administration of the H2-antagonist cimetidine may enhance the anticoagulant action of warfarin. Cimetidine, are thought to be potent inhibitors of P-450 enzymes because they can bind to both the oxygen and substrate binding sites of the enzymes.

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