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

Drug Elimination - Metabolism and Excretion Flashcards

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
Q

define cytochrome p450

A

cytochrome - coloured intracellular protein

450- contains heme pigment which absorbs light at 450nm when exopsed to co2

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26
Q

cytochrome p450 account for how much of the bodies metabolism

A

75%

27
Q

Reduction reaction are catalysed by which system and in which conditions is this most likely to occur

A

p450

anaerobic respiration

28
Q

Hydrolysis reaction are catalysed by …

A

Esterases and Amidases

29
Q

What is hydrolysis ?

A

splitting of drug molecule by addition of water

30
Q

Where does hydrolysis take place

A

plasma and tissues - small intestines mainly

31
Q

what is the name of the enzymes that carry out phase 2 reactions

A

transferases

32
Q

what is the name of the most common type of conjugation reaction

A

glucoronidation

33
Q

State some names of groups that are coupled to parent drugs or phase 1 metabolite

A 
glycine 
acetyl 
glucoronide 
glutathione 
sulphate 
methyl
amino acid
34
Q

paracetamol is also known as

A

aceteminophen

35
Q

what is a common cause of acute hepatic failure

A

paracetemol overdose

36
Q

Briefly explain what occurs when paracetamol is taken under normal doses

A

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
Q

What happens when paracetemol overdose occurs

A

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
Q

how can you stop NAPQI damaging the cells of the liver

A

administer acetylcysteine which helps restore availability of glutathione

39
Q

State factors which will affect drug metabolism

A 
enzyme inducer 
enzyme inhibitor 
age 
nutrition 
liver disease 
genetic variation
40
Q

What ids genetic polymorphism

A

inherited differences in the structures of the enzymes responsible for metabolism

41
Q

state two reasons why the first pass effect can be problematic

A

1 - larger doses needed orally than by other routes

2. big variation in extent of first pass effect - unpredictable

42
Q

what is a prodrug?

A

pharmacologically inactive when administered - remains like this until metabolised

43
Q

State some reasons why prescribing a prodrug may be appropriate

A

Related to solubility
Ensure duration of action is enhanced
Toxicity problems
drug needed to work at specific site

44
Q

give an example of a prodrug

A

Enalapril - enalaprilat

45
Q

What is excretion?

A

removal of a drug and its matabolites from the bosy

46
Q

what organ is responsible for excretion

A

kidneys

47
Q

state other routes available for excretion

A

saliva

breastmilk

48
Q

draw a simple illustration of the urinary system with labels

A

notes

49
Q

where does the kidney receive its blood supply from

A

renal arteries which branch from abdominal aorta

50
Q

state the role of the kidneys

A

filter blood
production of urine
regulate Ph of blood and regulate blood pressure
remove organic molecules form blood

51
Q

what part of the kidneys form an important part in the formation of urine

A

nephrons
85% - cortical nephrons located near cortex
15% juxta medullary nephrons - cortex medulla junction

52
Q

draw and label an image of kidney

A

notes

53
Q

draw , label and explain how a nephron functions

A

notes

54
Q

what restricts the passage of large molecules into the bowmans capsule

A

epithelial cells

55
Q

Blood arrives at the nephron via the

A

afferent arteriole

56
Q

What percentage of the plasma is filtered through the glomerulus

A

20%

57
Q

what are the names of the two systems that transfer the drug molecules into tubules

A

basic drugs

acidic drugs

58
Q

Active secretions is …

A

against the conc gradient

59
Q

What is passive reabsorption

A

drugs enter tubules but reabsorbed back into the blood
no energy required
diffusion

60
Q

basic drugs will be excreted in

A

acidic urine because low ph conditions favour ionisation of drug making it difficult to be reabsorbed

61
Q

acidic drugs will be excreted in

A

alkaline urine

62
Q

Renal excretion of drugs is affected by

A 
molecular weight of drug 
solubility of drugs 
Kidney disease
renal blood flow 
Age
Plasma protein binding
Dehydration
63
Q

what would cause drugs to be excreted via the faeces

A

if it wasnt absorbed following administration

64
Q

enterohepatic circulation

A

Notes

General Ocular Pharmacology (6 decks)

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