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ESA 2- Membranes and Receptors > Pharmokinetics 2 > Flashcards

Pharmokinetics 2 Flashcards

1
Q

Define pharmokinetics

A

What the body does to a drug

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2
Q

What are the possible fomulations of drugs?

A

Solid (tablet)

Liquid

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3
Q

What does the rate of action of a tablet depend on?

A

Dissolution

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4
Q

What is important to consider with formulation of drugs?

A

Patient compliance is important, and a once daily dose is easier

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5
Q

What are the possible sites of administration?

A

Local

Systemic

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6
Q

Give 3 examples of local sites of administration

A

Eye
Skin
Inhalation

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7
Q

What are the types of systemic adminisration?

A

Enteral

Parenteral

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8
Q

Give 3 examples of enteral sites of administration?

A

Sublingual
Oral
Rectal

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9
Q

Give 5 examples of parenteral sites of administration

A 
Subcutaneous injection 
Intramuscular injection 
Intravenous injection 
Inhalation 
Transdermal
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10
Q

What is oral bioavailability?

A

The proportion of a dose given orally (or by any other route other that intravenous) that reaches the systemic circulation in an unchanged form

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11
Q

What can bioavailability be expressed as?

A

Amount or rate

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12
Q

How is amount of bioavailability measured?

A

Area under curve of blood level vs time

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13
Q

How is rate of bioavailability measured?

A

By peak height and rate of rise of drug level in blood

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14
Q

How is bioavailability calculated?

A

(Area under curve oral / area under curve injected) * 100

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15
Q

What is the therapeutic ratio?

A

Maximum tolerated dose (LD50) / minimum effective dose (ED50)

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16
Q

What is the maximum tolerated dose?

A

The lethal dose to 50% of people

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17
Q

What is the minimum effective dose?

A

The effective dose in 50% of people

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18
Q

What happens to substances absorbed from the lumen of the ileum?

A

They enter the venous blood

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19
Q

Where happens to venous blood from the ileum drain?

A

It drains the hepatic portal vein, and is transported directly to the liver

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20
Q

What is the problem with drug absorbed from the ileum?

A

May give the first pass effect

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21
Q

What is the first pass effect?

A

The liver in the main site of drug metabolism, as it contains all of the necessary enzyme systems, so any drug absorbed from the ileum may be extensively metabolised during the first pass through the liver

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22
Q

How can the first pass effect be avoided?

A

Parenteral, sublingual or rectal routes

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23
Q

How much of an oral dose of paracetamol is metabolised by the first pass effect?

A

90%

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24
Q

What is drug distribution?

A

The theoretical volume into which a drug has distributed, assuming that this is occurring instantaneously

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25
Q

How is drug distribution calculated?

A

Amount given / plasma concentration at time 0

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26
Q

What do many drugs bind to?

A

Plasma protein

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27
Q

What of the drug exerts an effect?

A

The free level of drug (not the total)

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28
Q

Can protein binding actions occur?

A

Yes

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29
Q

When is drug binding to plasma proteins important?

A

If the drug is highly bound to albumin (>90%)
The drug has a small volume of distribution
The drug has a low therapeutic index

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30
Q

Give two examples of drugs where plasma protein binding is important

A

Warfarin

Tolbutamine

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31
Q

At what dose is an object drug (class I drug) used?

A

One that is much lower than the number of albumin binding sites

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32
Q

At what dose is a precipitant drug (class II drug) used?

A

One that is greater than the number of available binding sites

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33
Q

What happens when class I and II drugs are administered simultaneously?

A

Class I drugs are displaced by class II, raising the free levels of the object drug

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34
Q

What is the result of class II raising the free levels of the object drug?

A

High risk of toxicity

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35
Q

What are the precipitant drugs for warfarin?

A

Sulphanoamides
Aspirin
Phenytoin

36
Q

What are the precipitant drugs for tolbutamide?

A

Suphonamindes

Aspirin

37
Q

What is the precipitant drug for phenytoin?

A

Valproate

38
Q

What is the rate of metabolism if drugs are metabolised by enzymes that obey Michaelis-Menten kinetics?

A

(Vmax [C]) / (Km + [C])

39
Q

What is the rate of metabolism in a situation where a drug is used at a concentration that is lower than Km?

A

Vmax [C] / Km

40
Q

What kind of kinetics are being displayed when a drug is used at a concentration that is lower than Km?

A

First order

41
Q

What is happening in first order kinetics?

A

Metabolism is proportional to drug concentration

42
Q

What does first order kinetics give when a log scale is on the Y-axis versus time?

A

A straight line

43
Q

Can half life be defined with first order kinetics?

A

Yes

44
Q

Why can half life be defined with first order kinetics?

A

Because the rate of decline of plasma drug level is proportional to drug level

45
Q

What is the rate of metabolism in a situation where the drug is used at a concentration much greater than Km?

A

Vmax [C] / [C]

46
Q

What kind of kinetics are being displayed when a drug is used at a concentration much greater than Km?

A

Zero order

47
Q

Why are zero order kinetics displayed when the drug is used at a concentration much greater than Km?

A

Because the enzyme is saturated, and so the rate of decline of plasma drug level in constant, regardless of concentration

48
Q

What does zero order kinetics give when plasma concentration is plotted against time?

A

A straight line

49
Q

When will a steady state be reached during drug administration?

A

Within 5 half-lives of that drug

50
Q

What is required if an immediate effect of drug is necessary?

A

A loading dose

51
Q

What does first order kinetics give from dose increases?

A

A predictable therapeutic response

52
Q

What kind of response does zero order kinetic give?

A

A therapeutic response that can suddenly escalate as elimination mechanisms saturate

53
Q

How do most drugs behave?

A

With first order kinetics

54
Q

Give an example of a drug that displays zero order kinetics?

A

Alcohol

55
Q

What is the loading dose often determined by?

A

The volume of distribution

56
Q

What is true of most drug molecules?

A

They are stable and relatively unreactive

57
Q

What is a drug that is stable and relatively unreactive termed?

A

A pro-drug

58
Q

What happens in phase I of drug metabolism of the liver

A

A reactive group is exposed on the parent molecule, or added to the molecule

59
Q

What does phase I of drug metabolism generate?

A

A reactive intermediate that can be conjugated with a water-soluble molecule to form a water-soluble complex

60
Q

When is the reactive drug intermediate conjugated with a water-soluble molecule?

A

Phase II

61
Q

What are the most common chemical reactions in phase I of pro-drug metabolism by the liver?

A

Oxidation
Reduction
Hydrolysis

62
Q

What does the phase I process require?

A

A complex enzyme system called the cytochrome P450 (CYP) system, and a high energy cofactor (NADPH)

63
Q

What is true of the enzymes in phase I of drug metabolism in the liver?

A

They are inducible and inhibitable

64
Q

Give 3 examples of enzyme inducers involved in drug metabolism in the liver?

A

Phenobarbitone
Rifampicin
Cigarettes

65
Q

What drugs does phenobarbitone affect?

A

Warfarin

Phenytoin

66
Q

What drug does rifampicin affect?

A

Oral contraceptive

67
Q

What drug does cigarettes affect?

A

Theophylline

68
Q

Give an example of an enzyme inhibitor involved in drug metabolism in the liver?

A

Cimetidine

69
Q

What drugs does cimetidine affect?

A

Warfarin

Diazepam

70
Q

Why can some drugs bypass phase I?

A

They already have a reactive group on their molecule

71
Q

Give an example of a drug that can bypass phase I?

A

Morphine

72
Q

What happens in phase II of drug metabolism?

A

The reactive intermediate from phase I is conjugated with a polar molecule to form a water soluble-complex, in a process known as conjugation

73
Q

What is the most common phase II conjugate?

A

Glucoronic acid

74
Q

Why is glucoronic acid the most common phase II conjugate?

A

It’s an available byproduct of cell metabolism

75
Q

Other than glucoronic acid, what can drugs be conjugated with?

A

Sulphate ions

Glutathione

76
Q

What does phase II drug metabolism require?

A

Specific enzymes and a high energy cofactor, uridine diphosphate glucuronic acid (UDPGA)

77
Q

What is filtered through the glomerular tuft?

A

Only the free unbound drug

78
Q

What can actively secrete drugs?

A

The kidney tubule

79
Q

Give an example of a drug that can be actively secreted by a the tubule?

A

Penicillin

80
Q

What can determine how much of the drug is excreted?

A

Urine pH

81
Q

What affect will making the urine alkaline have on weakly acidic drugs?

A

It will make the drug ionised, so there will be less tubular absorption, because the charged drug stay in the tubular lumen, and so increased excretion

82
Q

Give an example of a weakly acidic drug?

A

Aspirin

83
Q

How can the pH manipulation of urine be clinically useful?

A

Forced alkaline diuresis in aspirin overdose

84
Q

What affect will acidic urine have on weakly basic drugs?

A

It will increase secretion

85
Q

Why will acidic urine increase secretion of weakly basic drugs?

A

Because it will ionise a weak base, making the charged drug stay in the tubule lumen

86
Q

Give an example of a weakly basic drug?

A

Amphetamine

ESA 2- Membranes and Receptors (13 decks)

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