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BRS YEAR 2 > Pharm - Principles of Pharmacology > Flashcards

Pharm - Principles of Pharmacology Flashcards

1
Q

What is pharmacology?

A

Study of drugs and drug action

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2
Q

What is therapeutics?

A

Concerned with drug prescribing - more patient focused

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3
Q

What is pharmacodynamics?

A

What a drug does to the body

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4
Q

What is pharmacokinetics?

A

What the body does to a drug

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5
Q

What are the 3 key questions of pharmacodynamics?

A

Where is the effect produced?
What is the target of the drug?
What is the response produced after interacting with the target?

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6
Q

Where is the effect of cocaine?

A

Dopaminergic neurones of the nucleus accumbent in the brain

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7
Q

What is the target of cocaine?

A

Dopamine reuptake protein

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8
Q

What is the response cocaine produces at the target?

A

Blocks reuptake of dopamine therefore causes euphoria

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9
Q

What are drug targets typically in the form of?

A

Proteins which are either activated or prevented from activating

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10
Q

What are the 4 main types of drug target

A

Ion channel
Transport protein
Enzyme
Receptor

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11
Q

In terms of selectivity, what causes side effects?

A

When drugs have lower selectivity, they are more likely to bind to other receptors therefore cause unintended side effects

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12
Q

How does drug dose relate to side effects?

A

Increasing the drug dose means that drugs are more likely to bind to similar receptors due to their degree of selectivity

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13
Q

What are the 4 main types of drug-target interaction?

A

Electrostatic
Hydrophobic
Covalent bonds
Stereoisomeric

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14
Q

What is the most common drug-target interaction?

A

Electrostatic

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15
Q

What are the 2 broad classes of drugs?

A

Agonists and antagonists

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16
Q

What is the affinity of a drug?

A

How strong it binds to a receptor

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17
Q

What is the binding of a drug to a receptor described as?

A

Transient binding to form a temporary drug-receptor complex

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18
Q

What is the efficacy of a drug?

A

Refers to the effect produced by a drug when bound to a receptor

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19
Q

What is an antagonist in terms of efficacy?

A

When a drug produces no effect when binding to a receptor

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20
Q

What is a partial agonist?

A

When a drug produces a partial response it has sub-maximal efficacy

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21
Q

What is a full agonist?

A

Drug produces the maximum effect on the receptor

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22
Q

What is the potency of a drug?

A

Concentration or dose of a drug required to produce a defined effect

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23
Q

How do we measure potency?

A

ED50 or EC50

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24
Q

What is EC50?

A

Half maximal effective concentration - what is the concentration of a drug needed to produce a 50% tissue response

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25
Q

What is ED50?

A

Half maximal effective dose - what is the dose needed to produce a 50% tissue response

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26
Q

What is a scenario whereby EC50 and ED50 differs?

A

E.g. if we are measuring an in vitro tissue sample, we can alter concentration to see a 50% tissue response. However, if we are testing a drug with people, we will change dose to see what dose produces a defined effect in 50% of people

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27
Q

Is potency the same as efficacy?

A

No

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28
Q

What is bioavailability?

A

How much of an administered drug ends up in the systemic circulation and thus is expressed as a percentage

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29
Q

What can determine bioavailability?

A

Site of administration

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30
Q

What are the common sites of administration?

A
  • IV
  • Intra nasal
  • Inhalation
  • Oral
  • Dermal (percutaneous)
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31
Q

When is bioavailability highest?

A

IV

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32
Q

How do drugs travel around the body?

A

Wither via bulk flow or diffusion in small groups of molecules

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33
Q

Why is IV 100% bioavailability but other administrations not?

A

IV is an example of bulk flow and is injected straight into the systemic circulation, other drugs travel by diffusion in small groups therefore need to pass at least 1 lipid membrane

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34
Q

What are the ways molecules travel across lipid membranes?

A

Pinocytosis
Diffusion via aqueous pores
lipid soluble diffusion
Carrier mediated transport

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35
Q

What is pinocytosis?

A

Membrane forming vesicle of chemical and releasing on other side (rare)

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36
Q

Why is diffusion via aqueous pores not common?

A

Most pores are less than 0.5nm wide, most drugs are larger than this

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37
Q

What is the most common diffusion method?

A

Lipid soluble diffusion

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38
Q

Why are drugs more commonly water soluble than lipid soluble?

A

Many are taken orally therefore need to be absorbed into aqueous environment of the GIT

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39
Q

What allows drugs to switch between solubilities?

A

Many drugs are weak acids or bases

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40
Q

What is aspirin an example of?

A

Weak acid

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41
Q

What does a weak acid do?

A

Donates protons when ionised

42
Q

What is morphine an example of?

A

Weak base

43
Q

What does a weak base do?

A

Accepts protons when ionised

44
Q

What are unionised drugs more capable of doing?

A

Retains more lipid solubility therefore more likely to diffuse

45
Q

What determines whether or not a drug is ionised?

A

pKa of the drug and the surrounding pH

46
Q

What happens when the pKa is equal to the pH?

A

50% is ionised and 50% unionised

47
Q

What is the typical pKa of weak acids>

A

3-5

48
Q

What is the typical pKa of weak bases?

A

8-10

49
Q

What happens to aspirin if the surrounding pH increases?

A

Ionised form dominates

50
Q

What happens to aspirin if the surrounding pH decreases?

A

Unionised form dominates

51
Q

What happens to morphine if the surrounding pH increases?

A

Unionised form dominates

52
Q

What happens to morphine if the surrounding pH decreases?

A

Ionised form dominates

53
Q

Where is a weak acid more unionised?

A

Acidic environment e.g. stomach acid

54
Q

Where is a weak base more unionised?

A

Blood and urine

55
Q

Why are weak bases poorly absorbed from the stomach?

A

Low pH leads to ionised form dominated therefore ion trapping

56
Q

What enables weak bases to be absorbed in the small intestine?

A

Large number of transport proteins in small intestine

57
Q

What stops ion trapping for weak acids?

A

In the blood. therefore are lots of transport proteins to stop ionised acid being trapped

58
Q

Where are the most important carrier systems for drug action found?

A

Renal tubule
Biliary tract
Blood brain barrier
GIT

59
Q

What factors affect tissue distribution of a drug?

A

Regional blood flow
Plasma protein binding
Capillary permeability
Tissue localisation

60
Q

Which tissues receive the most regional blood flow?

A 
Liver
Kidney
Muscles
Brain
Heart
61
Q

What can affect regional blood flow?

A

Exercise, or eating a large meal

62
Q

What is the most important plasma protein for binding

A

Albumin

63
Q

What is albumin particularly good at binding

A

Acidic drugs

64
Q

What determines the amount of drug that is bound?

A

Free drug concentration
Affinity for protein binding sites
Plasma protein concentration

65
Q

What is the blood conc of albumin?

A

0.6mmol/l

66
Q

What is the binding capacity of albumin?

A

1.2mmol/l

67
Q

Why are plasma proteins never saturated with drugs?

A

Because the required clinical effect for all drugs is achieved with a concentration less than 1.2mmol/l

68
Q

What drugs have the greatest affinity for plasma protein binding?

A

Acidic drugs

69
Q

What is the structure of most capillaries?

A

Continuous structure with endothelial cells aligned in a single file with small gap junctions between the cells

70
Q

What do most drugs need to be transported through the capillary

A

They need to be lipid soluble, if not then they will need transport proteins

71
Q

Why is the brain particularly hard to access?

A

Blood brain barrier has tight junctions between cells instead of H20 filled gap junctions

72
Q

Where is discontinuous capillary found?

A

Liver

73
Q

Where is fenestrated capillary found?

A

Kidney

74
Q

Why does the liver need discontinuous capillaries?

A

Highly metabolic therefore allows easy passage of drugs to diffuse in and out of the liver and the bloodstream

75
Q

Why does the kidney need fenestrated capillaries?

A

Key organ for excretion therefore allows small drugs to pass from blood to kidney tubules which will enhance the excretion of drugs

76
Q

Explain tissue localisation?

A

Lipid soluble drugs will more more heavily weighted to lipid areas such as the brain compared to the aqueous blood, contrast to water soluble drugs. This affects the proportion of a drug that is distributed to tissues

77
Q

What is the best solubility for excretion?

A

Water soluble

78
Q

What does drug metabolism involve?

A

Converting drugs to make them as water soluble as possible

79
Q

What are the main enzymes involved in drug metabolism?

A

P450 enzymes in the liver

80
Q

What is phase 1 metabolism?

A

Introduce a reactive group to the drug

81
Q

What is phase 2 metabolism?

A

Add a conjugate to the reactive group

82
Q

How can phase 1 metabolism occur?

A

Oxidation - most common
Reduction
Hydrolysis

83
Q

How do oxidation reactions occur?

A

Start with hydroxylation via p450 to incorporate oxygen into non activated hydrocarbons.
This gives us us metabolites with functional groups serving as a point of attack for conjugating systems of phase 2

84
Q

What are pro-drugs?

A

Parent drug has no activity - metabolism is required so that the metabolite has the pharmacological effect

85
Q

How does paracetamol cause liver damage?

A

Certain metabolite of paracetamol, not the drug itself

86
Q

What happens in phase 2 metabolism?

A

Attachment of a substituent group, and the resulting metabolite is nearly always inactive and far less lipid soluble compared to the phase 1 metabolite

87
Q

What are the main phase 2 enzymes?

A

transferases to transfer the substituent group to the phase 1 metabolite

88
Q

What is first pass (presystemic) metabolism?

A

Drugs that are absorbed by the GIT enter the hepatic portal blood supply where they will first pass through the liver and can be heavily metabolised reducing their activity.

89
Q

What is first pass metabolism a problem for?

A

Orally administered drugs

90
Q

What is the solution to first pass metabolism?

A

Administer a larger dose to ensure enough reaches the systemic circulation

91
Q

What is the problem with giving a larger dose to bypass first pass metabolism?

A

Extent of first pass metabolism varies from person to person therefore we don’t know how much drug we increase

92
Q

What are the ways in which drugs can be excreted

A

Lungs
Breast milk
Kidney (urine)
Liver (bile)

93
Q

What are the 3 routes for kidney excretion?

A

Glomerular filtration
Active tubular secretion (or reabsorption)
Passive diffusion across the tubular epithelium

94
Q

Why do drugs being excreted by the kidneys vary in their excretion?

A

As the extent to which drugs use different routes of excretion varies greatly in the kidneys

95
Q

What does glomerular filtration allow for?

A

Allows drug molecules of less than 20,000 molecular weight to diffuse into the glomerular filtrate, allowing a quicker rate of excretion than larger drugs

96
Q

Why is active tubular secretion the most important form of kidney excretion?

A

Only 20% of renal plasma is filtered at glomerulus, the rest (80%) passes onto the blood supply of the proximal tubule .

Proximal tubule capillary endothelial cells have 2 active transport carrier systems for acidic drugs and basic drugs against their concentration gradient

97
Q

What drugs are typically reabsorbed in the kidneys?

A

Drugs that are particularly lipid soluble

98
Q

What factors determine rate of drug reabsorption?

A

Drug metabolism - phase 2 metabolites less well reabsorbed

Urine pH - acidic drugs will be better reasborbed at lower pH and basic drugs at higher pH due to ionisation

99
Q

What is biliary excretion effective for removing?

A

Phase 2 glucuronide metabolites

100
Q

What does enterohepatic recycling do?

A

Significantly prolongs drug effect - glucuronide conjugate removed by gut bacteria, causing increased lipid solubility and thus greater reabsorption. The drug is then brought back to hepatic portal system, some is re-metabolised by the liver but some may escape to systemic circulation to have continued effects on the body

BRS YEAR 2 (37 decks)

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