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Biology > Receptor theory and pharmacokinetics > Flashcards

Receptor theory and pharmacokinetics Flashcards

1
Q

What is efficacy

A

A measure of a single agonist receptor complex’s ability to generate a response

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2
Q

What is the efficacy of an antagnoist

A

0

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3
Q

What is the efficacy of an agnonist

A

1

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4
Q

What is the concentration of a dug and the size of the response measured using

A

A bioassay using isolated cells

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5
Q

What does EC50 show

A

Defines the relationship between the drug and the response in that tissue

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6
Q

What is receptor reserve

A

100% of receptors don’t need to be occupied to give maximal response

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7
Q

Why is receptor reserve useful

A

Because the amount of hormones needed can be much lower

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8
Q

Which direction do spare receptors shift the response curve to

A

To the left of the binding curve

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9
Q

What will the efficacy of the agonist for its receptor influence

A

It will influence how big and how well it can produce responses

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10
Q

What is the hill slope equation

A

Response = max[Xa]^n/ ([Xa)n+[EC50]^n)
n is the hill slope factor, measure of the number of molecules that need to bind to a receptor to activate it

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11
Q

What does the drug with the highest potency require

A

The lowest concentration to produce 50% maximal response

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12
Q

What does the location of the concentration response curve depend on

A

Affinity, efficacy and spare receptors

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13
Q

What do agonists with different efficacies produce

A

Different maximal responses

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14
Q

What efficacy does a partial agonist have

A

between 0-1

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15
Q

What are partial agonists not able to produce

A

Not able to produce the same maximum response as a full agonist

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16
Q

What does a partial agonist need to achieve to produce the maximum response that it’s capable of?

A

100% occupancy

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17
Q

What are equal for partial agonists and why is this desirable

A

KD and EC50. You can’t get a maximum response for partial agonists so you can’t overdose

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18
Q

What 3 properties determine the effect of a drug in a living system

A

Specificity, affinity and efficacy

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19
Q

Definition of an antagonist

A

A drug that prevents the response of an agonist

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20
Q

What 5 classes can antagonism be divided into

A

Chemical, pharmacokinetic, physiological, non-competitive and competitive

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21
Q

What happens in chemical antagonism

A

Substances in a solution combine so that the effects of the active drug are lost

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22
Q

Example of chemical antagonism

A

Inactivation of heavy metals reduced with the addition of a chelating agent

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23
Q

What happens in pharmacokinetic antagonism

A

Refers to the processes that control the concentration of drugs in the body

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24
Q

Example of pharmacokinetic antagonism

A

some antibiotics stimulate the metabolism of warfarin so reducing its effective concentration in the blood stream

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25
Q

3 kinds of change as a result of pharmacokinetic antagonism

A

Change in drug metabolism, changes in excretion of an agonist, changes in absorption

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26
Q

What happens in physiological antagonism

A

The interaction of two drugs with opposing actions on the body

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27
Q

Example of physiological antagonism

A

Noradrenaline and adrenaline acting in the opposite way to histamine

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28
Q

What happens in non-competitive antagonism and how

A

Stop the agonist from having its signalling function by indirectly inhibiting the function of the signalling molecule or by binding somewhere different

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29
Q

What is a competitive antagonist

A

A drug that binds to a receptor to form a complex. It competes with an agonist for occupancy

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30
Q

How does competitive antagonism work

A

It enters the same site as the agonist, then stabilises the structure of the protein in a way that the activity is not induced

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31
Q

What is competitive antagonism dictated by

A

By the balance of the forward reaction and reverse reaction

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32
Q

What happens if we increase the concentration of the agonist in terms of competitive antagonism

A

We will increase the probability that an agonist will bind to the receptor compared to an antagonist

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33
Q

What happens to the concentration response curve with increasing levels of competitive antagonist

A

the further the shift to the right

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34
Q

What is dose ratio

A

How many more times agonist is needed in the presence of an antagonist

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35
Q

How do we calculate dose ratio

A

Concentration of agonist in presence of antagonist/ concentration of agonist in absence of antagonist

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36
Q

What does Schild analysis reveal

A

The affinity of the competitive antagonist for that receptor. It determines the affinity constant

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37
Q

What kind of scale/ graph is a Schild graph

A

Linear

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38
Q

What does the Y axis reveal on a Schild graph

A

Log value of the dose ratio - 1

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39
Q

What does the X axis reveal on a Schild graph

A

The log value of the concentration of antagonist that was added

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40
Q

What can we determine from the intercept of a Schild plot

A

The affinity

41
Q

How do we calculate Pa2

A

The intercept number multiplied by -1

42
Q

What does a larger PA2 value show

A

A higher affinity, more potency

43
Q

What do partial agonists behave like and which way do they shift the concentration response curve

A

Competitive antagonists and shift the curve to the right

44
Q

What is the difference between a partial agonist and a competitive antagonist

A

Partial agonists can induce some signalling in the absence of full agonists. Competitive antagonists don’t induce any signalling

45
Q

How do irreversible competitive antagonists work

A

They bind into the same sites as the agonists, but a chemical reaction occurs which creates a permanent bond

46
Q

How do we get rid of irreversible competitive antagonists

A

By creating new receptors

47
Q

What is pharmacodynamics based on

A

Based on the mechanism of action and effects on cellular functions e.g. receptors, ion channels, enzymes, transporters

48
Q

What do the physiochemical properties of drugs affect

A

Affinity, efficacy and potency

49
Q

In pharmacokinetics, what do the physiochemical properties have an impact on

A

Absorption, diffusion, metabolism and excretion (ADME)

50
Q

What is the main way drugs are delivered around the body

A

Bulk flow in plasma

51
Q

What does bulk flow depend on

A

The cardiovascular system

52
Q

What’s the first factor we need to consider in terms of drug absorption

A

How they diffuse across the plasma membrane

53
Q

What is the diffusion coefficient and what does it mean

A

1/ sqr of its molecular weight.
The larger the molecular weight, the slower its diffusion

54
Q

What are the 4 main mechanisms drugs have to get through the plasma membrane

A

Diffusion through lipids, diffusion through aqueous pore, carriers/ transport proteins, bulk flow by pinocytosis

55
Q

What is lipid solubility defined by

A

Partition coefficient

56
Q

What is the partition coefficient

A

How readily a molecule dissolves in water versus oil

57
Q

What is diffusivity defined by

A

Diffusion coefficient

58
Q

Why are drugs weak acids/ bases

A

They readily form salts so its easier to package them into a tablet/ liquid

59
Q

What does the Henderson Hussle Puc equation describe

A

The relationship between the charged and unchanged form of a weak acid or base

60
Q

What is the Henderson Hussle Puc equation

A

pKa= pH + log10(HA/A-)

61
Q

What is the pKA value of weak acids

A

below 7

62
Q

What is the intravenous route of administration

A

Intravenous route, injecting straight in, used in emergancy situations

63
Q

What is the intramuscular injection used for

A

Administering molecules that are protein in nature e.g. insulin

64
Q

What is the intrathecal route of administration

A

Direct lumber puncture into the cerebral spinal fluid so it has rapid action to the central nervous system.

65
Q

What is the inhalation route of administration

A

Used and restricted to drugs localised in the lung where the molecule is a gas

66
Q

What is the percutaneous route of administration

A

Administering the drug directly through the skin, avoids the metabolism in the gut

67
Q

What is the percutaneous route of administration

A

Administering the drug directly through the skin, avoids the metabolism in the gut

68
Q

What is the oral route of administration and what do you need to consider

A

Oral is swallowing tablet. Need to consider the particle size

69
Q

What is bioavailability

A

Only a fraction of ingested dose gains access to circulation

70
Q

What are the overall factors affecting absorption

A

Site/ method of administration, molecular eight, lipid solubility, pH and ionization

71
Q

What % of body weight does plasma make up

A

4.5%

72
Q

What % of body weight does interstitial fluid make up

A

16%

73
Q

What % of body weight does lymph make up

A

1-2%

74
Q

What % of body weight does intracellular fluid make up

A

30-40%

75
Q

What % of body weight does transcellular fluid make up

A

2.5%

76
Q

What % of body weight does fat make up

A

20%

77
Q

What is the volume of distribution of a drug

A

A measure of the volume of fluid that would be required to hold the amount of drug in the body as measured in the plasma

78
Q

What is the volume of distribution equation

A

Vd= Dose/ CP

79
Q

Which drugs have a high volume of distribution

A

Propranolol and ethanol

80
Q

Which drugs have a low volume of distribution

A

Herapin

81
Q

What is meningitis

A

The breakdown of tight junctions in the brain caused by a bacterial infection

82
Q

How can we treat meningitis

A

IV penicillin

83
Q

What other factors influence drug distribution and example

A

Binding to plasma proteins e.g. albumin binds mainly acidic and highly charged proteins

84
Q

What does body fat act as

A

Acts as a reservoir on the drug causing the drug to stay in the body for longer

85
Q

Where does metabolism take place

A

In the liver

86
Q

What is the phase 1 reaction of metabolism

A

Catabolic reaction- changes the composition of the drug to produce a more active compound

87
Q

What is the phase 2 reaction of metabolism

A

Anabolic reaction - involves the conjugation of large molecules with a more reactive compound to produce inactive product

88
Q

What are the enzymes involved in metabolism

A

Microsomal

89
Q

What are the largest family of microsomal enzymes

A

Cytochrome P450

90
Q

What are prodrugs

A

When the molecule in the phase 1 reaction may still have activity

91
Q

What are the factors influencing drug metabolism

A

Route of administration

92
Q

What is the most common way of eliminating drugs

A

Metabolism of the liver

93
Q

What occurs during the elimination of aspirin

A

1: Hydroxylation reaction at the acetyl group carried out by cytochrome p450 enzyme
2: Salicylic acid is conjugated with glucuronide which is transported through the body via bulk flow

94
Q

How many genes in the human genome can code for the p450 enzymes

A

57

95
Q

What can you not take while taking warfarin and why

A

Grape fruit juice because it inhibits the activity of the enzyme involved in warfarin

96
Q

What do different isoforms of P450 do

A

They react with different drugs

97
Q

What do inducers of P450 do

A

Increase drug metabolism and therefore lower the plasma concentrations of the drug to the point where it can’t achieve therapeutic concentrations

98
Q

Types of renal excretion

A

Glomerular filtration, active tubular secretion, passive diffusion

99
Q

Is diazepam cleared quickly or slowly and why

A

Highly lipophilic, so active metabolites are cleared slowly

Biology (9 decks)

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