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General Ocular Pharmacology > Drug Elimination - Metabolism and Excretion > Flashcards

Drug Elimination - Metabolism and Excretion Flashcards

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1
Q

What is Drug metabolism ?

A

is the biochemical modification of substances , in this case drug which is performed by specialist enzymes.

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2
Q

What is another term for drug metabolism ?

A

Xenobiotic Metabolism.

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3
Q

What is the ultimate aim of metabolsim?

A

most drugs are lipophilic which makes it difficult to excrete so metabolism converts them into hydrophilic molecules which will help the drug be excreted into the urine.

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4
Q

As drugs are metabolised the therapeutic effect decreases , is this true?

A

Yes for some drugs however there are some drugs will becomes active only after metabolism occurs - these are called prodrugs.

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5
Q

What are the products of the chemical reactions that take place in metabolism

A

Metabolites

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6
Q

Explain the two ways in which drug metabolism can be bought about by?

A
  1. Specialist Mechanisms - if drug is similar to another substance already in the body like a neurotransmitter the it will be broken down by specialist mechanisms eg - adrenaline = monoamine oxidase
  2. General Mechanisms - most drugs metabolised by enzymes present in the smooth endoplasmic reticulum of the liver.
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7
Q

What is microsomal metabolism

A

To reach SER of liver drugs need to be lipophilic = the products of the reaction = hydrophilic = process known as MM.

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8
Q

Where in the body is main site for drug metabolism?

A

Liver
- highly metabolically active
- large organ size
supplied with blood which contains most of absorbed drug from GI tract via hepatic portal system
- high conc of enzymes compared to other parts of the bosy.

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9
Q

State other sites of metabolism in the body

A

Wall of intestines
lungs
kidneys
plasma

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10
Q

What do you know about the liver?

A
  • 1.5kg
  • 4 lobes of unequal size and shape
  • overlies the gallbladder which stores bile synthesized by liver
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11
Q

Where does the liver receive blood from?

A

oxygenated blood via hepatic artery

deoxygenated via hepatic portal vein.

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12
Q

blood drains from the liver by the

A

hepatic vein

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13
Q

Liver is made up of …

A

collection of hepatic lobules

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14
Q

Describe structure of a lobule

A

hexagonal
have central vein which leads ot hepatic vein - carry blood away from liver
each corner of lobule there are collection of structures

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15
Q

In each corner of lobule there are collection of structures - State what they are

A 
branch of hepatic artery 
branch of hepatic portal vein 
bile duct 
lymphatic vessels 
branch of vagus nerve
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16
Q

what is a sinusoid

A

channels (enlarged capillaries)running through the lobule

blood flows from hepatic portal vein and artery in the corners of lobules draining it into the central vein

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17
Q

What surround the sinusoids

A

liver cells - hepatocytes

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18
Q

what is the main function of the smooth endoplasmic reticulum

A

biosynthesis of the phospholipids and cholesterol

hepatocytes - metabolism because it contains large amount of enzyme family - cytochrome p450

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19
Q

How many phases f metabolism are they and what are they names

A 
two phases 
1. Functionalisation
includes oxidation , reduction hydrolysis  
2. Conjugations 
with charged species
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20
Q

What is the purpose of phase 1 reactions

A

exposing or introducing a functional group - such as hydroxy; , amino or carboxyl
this will increase reactivity of the drug and slightly increase the hydrophilicity

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21
Q

What is the purpose of phase 2 reactions

A

metabolites are conjugated with charged species such as sulphate , glycine, glucuronic acid which will strongly increase hydrophilicity
attachment of ionised group will make it more water soluble

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22
Q

What is oxidation ?

A
  • most common phase 1 reaction
  • its the addition of a single o2 atom to drug moecule to form an OH(hydroxyl group)
  • catylsed by cytochrome p450 in liver
  • omeprazole ( used in tx of gastric disease)
  • o2 split - one added to substrate and one combined with hydrogen to produce water
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23
Q

What does oxidation require to take place

A

molecular oxyGen and NADPH nicotinamide adenine dinucleotide phosphate

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24
Q

Where is cytochrome p450 located

A

within cells - mitochondria or ER

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25
define cytochrome p450
cytochrome - coloured intracellular protein | 450- contains heme pigment which absorbs light at 450nm when exopsed to co2
26
cytochrome p450 account for how much of the bodies metabolism
75%
27
Reduction reaction are catalysed by which system and in which conditions is this most likely to occur
p450 | anaerobic respiration
28
Hydrolysis reaction are catalysed by ...
Esterases and Amidases
29
What is hydrolysis ?
splitting of drug molecule by addition of water
30
Where does hydrolysis take place
plasma and tissues - small intestines mainly
31
what is the name of the enzymes that carry out phase 2 reactions
transferases
32
what is the name of the most common type of conjugation reaction
glucoronidation
33
State some names of groups that are coupled to parent drugs or phase 1 metabolite
``` glycine acetyl glucoronide glutathione sulphate methyl amino acid ```
34
paracetamol is also known as
aceteminophen
35
what is a common cause of acute hepatic failure
paracetemol overdose
36
Briefly explain what occurs when paracetamol is taken under normal doses
converted into non toxic metabolites by phase 2 metabolism conjugation reactions occur with sulphate and glucoronide small amount metabolised to create highly reactive intemediate metabolite known as NAPQI UNDER NORMAL - napqi IS CONJUGATED WITH GLUTATHIONE
37
What happens when paracetemol overdose occurs
sulphate and glutathione pathways becomes saturated only other route to metabolise is to produce more NAPQI all of glutathione will be used up NAPQI will begin damaging the cells of liver
38
how can you stop NAPQI damaging the cells of the liver
administer acetylcysteine which helps restore availability of glutathione
39
State factors which will affect drug metabolism
``` enzyme inducer enzyme inhibitor age nutrition liver disease genetic variation ```
40
What ids genetic polymorphism
inherited differences in the structures of the enzymes responsible for metabolism
41
state two reasons why the first pass effect can be problematic
1 - larger doses needed orally than by other routes | 2. big variation in extent of first pass effect - unpredictable
42
what is a prodrug?
pharmacologically inactive when administered - remains like this until metabolised
43
State some reasons why prescribing a prodrug may be appropriate
Related to solubility Ensure duration of action is enhanced Toxicity problems drug needed to work at specific site
44
give an example of a prodrug
Enalapril - enalaprilat
45
What is excretion?
removal of a drug and its matabolites from the bosy
46
what organ is responsible for excretion
kidneys
47
state other routes available for excretion
saliva | breastmilk
48
draw a simple illustration of the urinary system with labels
notes
49
where does the kidney receive its blood supply from
renal arteries which branch from abdominal aorta
50
state the role of the kidneys
filter blood production of urine regulate Ph of blood and regulate blood pressure remove organic molecules form blood
51
what part of the kidneys form an important part in the formation of urine
nephrons 85% - cortical nephrons located near cortex 15% juxta medullary nephrons - cortex medulla junction
52
draw and label an image of kidney
notes
53
draw , label and explain how a nephron functions
notes
54
what restricts the passage of large molecules into the bowmans capsule
epithelial cells
55
Blood arrives at the nephron via the
afferent arteriole
56
What percentage of the plasma is filtered through the glomerulus
20%
57
what are the names of the two systems that transfer the drug molecules into tubules
basic drugs | acidic drugs
58
Active secretions is ...
against the conc gradient
59
What is passive reabsorption
drugs enter tubules but reabsorbed back into the blood no energy required diffusion
60
basic drugs will be excreted in
acidic urine because low ph conditions favour ionisation of drug making it difficult to be reabsorbed
61
acidic drugs will be excreted in
alkaline urine
62
Renal excretion of drugs is affected by
``` molecular weight of drug solubility of drugs Kidney disease renal blood flow Age Plasma protein binding Dehydration ```
63
what would cause drugs to be excreted via the faeces
if it wasnt absorbed following administration
64
enterohepatic circulation
Notes

General Ocular Pharmacology (6 decks)

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