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3. Pharmokinetics. Absorption. > Absorption. > Flashcards

Absorption. Flashcards

1
Q

What are ABC transporters?

A

ATP Binding Casettes, these transporters require energy from ATP in order to function.

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2
Q

What is meant by the term absolute bioavailability?

A

When all of an injected drug enters circulation.

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3
Q

What form of drug administration is the only way of reaching the absolute bioavailability?

A

Intravenous administration.

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4
Q

What is active transport?

A

When compounds are transported across cell membranes via transport proteins.

This form of transport always requires energy.

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5
Q

What is the ionised form of a drug?

A

The form of a drug that is charged.

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6
Q

What is facilitated diffusion?

A

Diffusion that occurs through specific membrane proteins.

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7
Q

Define diffusion?

A

When a substance moves into a cell via a concentration gradient, from high concentration to low concentration.

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8
Q

What is the non-ionised form of a drug?

A

The form of a drug that is uncharged.

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9
Q

Define paracellular transport?

A

Where substances move through the gaps that are found between cells.

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10
Q

Define pH?

A

A measure of the hydrogen ion concentration in a solution to determine its acidity or alkalinity.

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11
Q

Define the pKa?

A

The negative log of the acid dissociation constant.

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12
Q

How does a low pKa affect the strength of an acid?

A

The lower the pKa, the stronger the acid.

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13
Q

Define the relative bioavailability of a drug?

A

The bioavailability of a drug administered in one way relative to its bioavailability following another route of administration.

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14
Q

What is the site of action?

A

The location where the drug needs to act e.g. the site of infection.

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15
Q

What is the absorption of drugs?

A

The passage of drugs from an injection site to the site of injury.

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16
Q

What must most drugs enter before they can reach their site of action?

A

Plasma.

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17
Q

What drugs do not have to enter the plasma before they reach their site of action?

A

Local drugs.

Drugs that lead to vasoconstriction or vasodilation.

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18
Q

What are the 3 ways that drugs which undergo passive diffusion can diffuse through the intercellular spaces?

A

Paracellular transport.

Diffusion.

Facilitated diffusion.

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19
Q

How do drugs that undergo active transport enter the tissues?

A

Via cellular transporters.

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20
Q

What kind of transporters will remove drugs from the tissues and transport them back into the blood?

A

ABC transporters.

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21
Q

What happens if a drug is an intracellular substrate for an ABC transporter?

A

It will be removed from the cell and the drug concentration will go down.

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22
Q

Why do we want to design our drugs so that they are not recognised as intracellular substrates by ABC transporters?

A

So they will be removed from the cell.

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23
Q

Do ABC transporters bring substances into the tissues?

A

Yes, they can bring substances in and out of the tissues.

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24
Q

What are 3 characteristics about the drug that will influence its rate of absorption?

A

Drug pKa.

Drug size.

Whether the drug is lipophilic etc.

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25
Q

What are 3 characteristics about the patient that will influence its rate of absorption?

A

Their metabolism.

Their organ perfusion.

Their plasma protein concentrations.

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26
Q

Will the disease affect the rate of drug absorption?

A

Yes.

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27
Q

Will the route of administration affect how quickly the drug is absorbed?

A

Yes.

E.g. The site of injection will heavily influence how the drug is absorbed.

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28
Q

What methods of drug administration will have instant absorption?

A

Anything that injected intramuscularly or subcutaneously.

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29
Q

Why does any drug that is orally administered have a delayed absorption time?

A

As it takes time for substances to travel through the GI tract.

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30
Q

What orally administered substances will have a very quick absorption time?

A

Substances that are absorbed in the mouth.

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31
Q

Where can substances given via oral administration be absorbed?

A

Anywhere in the GI tract (from the mouth to the large intestine).

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32
Q

Can the passive transport/absorption of a drug be stopped?

A

No.

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33
Q

Can the active transport/absorption of a drug be stopped?

A

Yes, if we inhibit the transporter proteins.

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34
Q

What does the passive transport/absorption of drugs depend on?

A

On a concentration gradient.

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35
Q

What form of transport/absorption is concentration independent?

A

Active transport.

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36
Q

Why is the active transport of drugs concentration independent?

A

As the transporter proteins will transport any amount of drug across the cell membrane.

37
Q

What must any drug that uses active transport have?

A

A structure that fits into the transport proteins.

38
Q

What are the 4 characteristics of passive transport?

A

Concentration dependent.

Cannot be inhibited.

Not structure specific.

Not cell type specific.

39
Q

What are the 4 characteristics of active transport?

A

Concentration independent.

Can be inhibited.

Structure specific.

Cell type specific.

40
Q

How will drug absorption be affected if the patient has just had a meal?

A

Absorption may take longer.

Some drugs may bind to food and not be absorbed.

41
Q

How will drug absorption be affected in an animal that has diarrhoea?

A

The gastro-intestinal motility will be increased and the drug will pass through the GI tract.

42
Q

What is the major determinant of drug absorption in the GI tract?

A

The blood flow at the GI tract.

43
Q

What 5 things determine the absorption of orally administered drugs?

A

Whether the stomach is empty or full.

Gastro-intestinal motility.

Blood flow to the GI tract.

Drug particle size and formulation.

Drug interactions.

44
Q

Any drugs that can diffuse across cell membranes must have what characteristic?

A

They must be lipophilic.

45
Q

Will hydrophilic substances be absorbed into cells via diffusion?

A

They are unlikely to be absorbed by diffusion as they cannot pass the lipid bilayer.

46
Q

Can hydrophilic substance cross the cell membrane via active diffusion?

A

Yes.

47
Q

Are lipophilic or hydrophilic substances more or less likely to be broken down in the GI tract?

A

Lipophilic substances are less soluble and will not be broken down in the GI tract.

48
Q

What does the permeability co-efficient (P) tell us?

A

How easy it is for a drug to travel across a membrane.

49
Q

What are the characteristics of a drug with LOG P = 0?

A

The drug has hydrophilic and lipophilic characteristics.

This means it dissolves easily in the GI tract and passes the through the lipid bilayer.

50
Q

What are the characteristics of a drug with LOG P = is negative?

A

Then the drug is hydrophilic.

This drug will not be absorbed by the bilayer, but it will dissolve in the GI tract.

51
Q

What are the characteristics of a drug with LOG P = is positive?

A

The drug will be lipophilic.

There will be limited absorption depending on how lipophilic the drug is.

52
Q

What are very lipophilic drugs unlikely to be absorbed into the cell?

A

As it is more likely it is that the drug will remain in the lipid bilayer.

53
Q

What is the absorption time of a drug with a positive LOG P?

A

Anything with a positive LOG P will have delayed absorption time.

54
Q

Drugs with what LOG P have good absorption?

A

Drugs with LOG P = 0.

55
Q

Drugs with what LOG P have poor absorption?

A

Drugs with a negative LOG P?

56
Q

Drugs with what LOG P have delayed and limited absorption?

A

Drugs with a positive LOG P?

57
Q

What is determined by the rate of dissociation of the drug?

A

The rate of absorption.

58
Q

What is the pH in the intestinal lumen?

A

Above 7.

59
Q

Can dissociated (ionised) drugs pass through membranes?

A

No as dissociated drugs tend to be hydrophilic.

60
Q

Can undissociated (non-ionised) drugs pass through membranes?

A

They are very likely to pass through a membrane.

61
Q

What determines whether a drug dissociates?

A

The pH of the tissue where the drug is.

The pKa of the drug.

62
Q

Are most drugs acids or bases?

A

Most drugs are weak acids or bases.

63
Q

What tells us whether a drug will dissociate at a certain pH?

A

The Henderson Hasselbach equation.

64
Q

If the pKa of the drug is similar to the pH of the location where the drug what will the acid base concentration of the drug be?

A

It will be 50/50 as half of the drug is ionised and half is non ionised.

65
Q

What is the non-ionised form a drug always bound to?

A

A hydrogen atom.

66
Q

Will the charged or uncharged form of a drug be able to pass through membranes?

A

The uncharged form of the drug can pass through membranes, but the charged form cannot.

67
Q

Will a drug that is a weak base be absorbed in the stomach?

A

No.

The stomach is an acidic environment and the drug will be ionised in this environment.

68
Q

What happens if a drug that is a weak base is administered orally?

A

It will ionise in the stomach and not be absorbed.

Once it reaches the intestines the pH increases and the drug will de-ionise and can then be absorbed.

69
Q

When will an acidic drug be ionised?

A

If the pH is 3 units higher than the pKa (an acidic drug in a basic environment).

70
Q

What happens if we put a drug that is a weak acid in an acidic environment?

A

It will be non-ionised and this means it can be absorbed.

71
Q

What happens if we put a drug that is a weak base in an acidic environment?

A

It will be ionised.

72
Q

What happens if we put a drug that is a weak base in an basic environment?

A

Then it will be non-ionised.

73
Q

What about the pH and pKa will determine how likely it is for a drug to be absorbed?

A

The closer the pKa is to the physiological pH the more likely it is that the drug will be absorbed.

74
Q

What 3 categories determine drug transport across membranes?

A

The drug.

The physiological parameters.

The patient parameters.

75
Q

Why is it very important that the drug is stable in the environment that we are administering it into?

A

Otherwise it will be useless.

76
Q

Will areas that are well perfused have better or worse drug absorption than areas that are badly perfused?

A

Areas that are well perfused have better absorption.

77
Q

What must be present for diffusion to occur?

A

A concentration gradient.

78
Q

Why is active transport slower than passive transport?

A

As transport proteins can only transport a certain amount of substance per unit of time.

Diffusion is quicker as more substance crosses a barrier in the time it takes for a transport protein to bring in 1 molecule.

79
Q

What determines the rate of diffusion?

A

The amount of drug that is administered.

The more drug administered gives a higher diffusion rate as there is a larger concentration gradient.

80
Q

ABC drug transporters will prevent the absorption of what substances?

A

Certain types of toxin and xenobiotics as the moment they go through the membrane they are immediately removed.

81
Q

Is ABC transport an active or passive form of transport?

A

An active form.

82
Q

Why does a large percentage of drug get absorbed despite removal of drug by ABC transporters?

A

As active transport takes time.

This means some drug can absorbed, even though a percentage is not thanks to the ABC transporters.

83
Q

Are ABC transporters present in many tissues?

A

Yes.

84
Q

What is the bioavailability of the drug?

A

The proportion of the drug that reaches the plasma.

85
Q

The bioavailability of the drug is always 100% following what route of administration?

A

Intravenous administration.

86
Q

Will the formulation of the drug will have a huge effect on its bioavailability?

A

Yes.

E.g. A drug that is one form may be much easier to absorb than a drug in another form.

87
Q

Does the amount of food in the GI tract affect drug absorption?

A

Yes.

Some drugs can be absorbed straight after a meal.

Other drugs will have limited absorption if they are taken right after a meal.

Some drugs must be taken with food as they will not be absorbed unless there is food in the GI tract.

88
Q

What does relative bioavailability allows us to calculate?

A

The bioavailability of a drug that has been administered in one way relative to the bioavailability of the same drug that is administered in another way.

This allows us to compare routes of administration and determine which route provides the best bioavailability for a drug that cannot be injected intravenously.

3. Pharmokinetics. Absorption. (1 decks)

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