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BMS242 Core Phys Pharm > L9-10 Pharmacokinetics > Flashcards

L9-10 Pharmacokinetics Flashcards

1
Q

Drug effects depend on

A

Mechanism of action
Physiochemical properties of drugs
Concentration

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2
Q

What are the physiochemical properties of drugs

A

Affinity
Efficacy
Potency

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3
Q

What are the four elements which affect drug concentration

A

Absorption
Distribution
Metabolism
Excretion

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4
Q

Bulk flow of drug uses what

A

The CV system

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5
Q

4 methods of drug movement across cell membranes

A

Simple diffusion
Diffusion through aqauporins
Carrier
Pinocytosis

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6
Q

What are the physiochemical properties of the drugs

A

Lipid solubility

Diffusivity

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7
Q

What constant can be used to quantify lipid solubility

A

Partition coefficient

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8
Q

What constant can be used to quantify diffusivity

A

Diffusion coefficient

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9
Q

What type of molecules dissolve freely in lipids and penetrate cell membranes freely

A

Lipid soluble

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10
Q

What would the effect of using a lipid soluble molecule on rate of absoption from gut be

A

Increase

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11
Q

What would the effect of using a lipid soluble molecule on penetration of the brain and other tissues

A

Increase

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12
Q

What would the effect of using a lipid soluble molecule on renal elimination

A

Increase

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13
Q

What is is one of the most important determinants for pharmacokinetic characteristics of the drug

A

Lipid solubility

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14
Q

Describe intravenous administration

When might it be used

A

Injection straight into the plasma

In emergencies

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15
Q

What drugs may need to be administered intra muscularly

A

Drugs that would be at high risk of being metabolised in the gut

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16
Q

What types of drugs may be at high risk of being destroyed in the gut

A

Peptides

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17
Q

Give an example of a peptide drug

A

Insulin

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18
Q

What does intrathecal inject into

A

Direct into the CSF

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19
Q

Give an example of when intrathecal admin. may be used

A

During labour to administer local anasthetics

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20
Q

Define bioavailability

A

How much of the injected drug will make it into the plasma

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21
Q

What must be overcome in the stomach

A

Low pH

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22
Q

What is the portal system, what is the danger if drugs enter

A

Involving the liver

Drugs would be metabolised by the liver

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23
Q

What can be controlled with a drug in tablet form

A

The rate at which the active form of the drug is liberated from the tablet

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24
Q

When may the oral route be unsuitable

A

When vomitting
GI problems - ulceration
Young children may find it hard to swallow

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25
Q

If the drug target was the GI tract what would be the favoured method of administration

A

Rectal route

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26
Q

What is usually the difference between cheaper and more expensive over the counter drugs

A

Particle size - tends to be larger with cheaper drugs

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27
Q

What is percutaneous administration

A

Absoprtion through the skin

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28
Q

Example of a drug that is adminstered percutaneously

A

Nicotine via patches

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29
Q

What is the problem with percutaneous administration

A

Skin is highly impermeable

Drug would need to have a high lipid solubility

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30
Q

What would the targets of drugs be that were adminsistered percutaneously

A

Nuclear receptors

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31
Q

example of a type of drug that would be administered percuansouslt

A

Hormone

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32
Q

What two classes of drug are administered by inhalation

A

General anasthetics and drugs which target the lungs

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33
Q

What sort of molecules would cross the placenta

A

lipophilic (soluble in lipids)

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34
Q

Most drugs are weak X and X

A

Acids and bases

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35
Q

Difference between a weak and strong acid

A

Strong - fully dissociate

Weak - partially dissociate

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36
Q

Describe the dissociation for a weak acid

A

HA <==> A- + H+

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37
Q

What does pKa represent

A

The pH at which 50% of the acid is in its disociated form

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38
Q

State the Henderson-Hasslebach equation

A

pKa = pH + log (HA/A-)

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39
Q

What can be said about weak acids at a low pH

A

They will be undissociated

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40
Q

What can be said about weak acids at a high pH

A

They will be dissociated

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41
Q

pKa of aspirin

A

3.5

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42
Q

Aspirin has a pKa of 3.5, state what will happen in the following

Gastric juices at pH 3

Plasma at pH 7.4

Urine at pH 8

A

gastric juices, pH low therefore undisociated and able to move freely across the membranes

Plasma pH is higher therfore more will dissociated

In urine pH much higher therfore lots dissociated and it is trapped

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43
Q

How can the weak acids become trapped

A

Undissoicated HA form is non polar so can diffuses across the membrane
Once dissociated both A- and H= have charge, so these are not able to cross the membrane

44
Q

What can be used to treat aspirin poisoning

A

Increasing the plasma pH by adding HCO3-, weakly acidic drugs are drawn out of the CNS into the plasma where they become trapped

45
Q

Two types of carrier mediated transport

A 
Solute carrier (SLC) transport 
ATP binding cassettes (ABC) transporters
46
Q

SLC transport is

A

Passive

47
Q

ABC transport is

A

Active

48
Q

Two consideration to consider for rate at which drug is able to be transported across the cell membrane

A

Number of channels in the membrane

MAX rate that these channels are able to function at

49
Q

What two considerations must be made for normal physioligcal fucntion if a large ammount of drug has to be transported across a membrane

A

Build up on one side if rate is slow

Impact on transport of the endogenous drugs

50
Q

What is OCT1

A

Organic cation transporter 1

51
Q

What is metformine

A

Drug used to treat type 2 diabetes

52
Q

What do genetic variants of OCT1 show when treated with metformin

A

Different response effects due to single nucleotide polymorphisms (SNPs)

53
Q

4 major body compartments

A

ECF
ICF
Transcellular
Fat

54
Q

3 compartments of the ECF

A

Plasma
Interstitial fluid
Lymph

55
Q

Conc of plasma to b.w.

A

4.5%

56
Q

Two things that determine the distribution of a drug

A

Permeability and lipid solubility

57
Q

What compartment are non polar drugs able to enter easily

A

Fat compartment

58
Q

Why does drug entering fat cause problems for people with varying body masses

A

Ammount of drug entering the fat compartment can vary so concentration of drug in the plasma will vary also

59
Q

What protects the fetus

A

Placenta

60
Q

What prevents the CNS from drugs

A

bbb

61
Q

What type of cell junction are involved in the formation of the blood brain barrier

A

Tight junctions between endothelial cells

62
Q

What is the BBB impermeable to

A

Impermeable to H20 soluble molecules

63
Q

Give an example of two substances that the BBB would be impermeable to

A

Peptides, antibiotics

64
Q

What type of molecules are able to cross the BBB, give two examples

A

Lipid soluble molecules

Ethanol and caffine

65
Q

What happens to the BBB during inflammation, what disease does this occur in and how may it be treated

A

Tight junctions become leaky
E.g. in meningitus
Can treat with IV penicillin ==> able to pass through the BBB due to the leaky tight junctions

66
Q

Define the chemoreceptor trigger zone

A

An area of the medulla that recieves inputs from blood borne drugs and hormones and is able to initiate vomitting

67
Q

What NT has receptors in the chemoreceptor tirgger zone

A

Dopamine

68
Q

What extra precaution must be taken when treating Parkinsons with dopamine

A

Dopamine may also be an agonist in the chemoR trigger zone
Should be given with a dopamine antagonist which is also not able to cross the BBB and therefore is unable to cause vomitting

69
Q

Albumin is what? What is it able to do?

A

Plasma protein

May bind to drugs

70
Q

Drugs that are bound to albumin are not

A

Filtered

71
Q

What is the binding capacity of albumin

A

1.2mmol

72
Q

What is the affect of albumin binding to a drug

A

It would reduce the concentration of free drug in the plasma

73
Q

What must be taken in consideration when a high concentration of drug is required for the response but plasma protein binding occurs

A

If binding occurs then won’t be as high conc of free drug in the blood ==> response may not be seen

74
Q

What would possibly be the implications if a person was taking more than drug which is known to bind to plasma proteins

A

One drug will outcompete and displace the other from binding causing the concentrations of drug in the blood to vary dramatically

75
Q

Issues with prescribing a drug to someone with low body fat

A

Effects can be longer lasting as less is partitioned into the fat compartment
Drug concentration reaching target very high ==> as no reservoir to mop up the drug

76
Q

Phase 1 reaction anabolic or catabolic

A

Catabolic

77
Q

What does a phase 1 reaction produce

A

More reactive compounds

78
Q

Phase II reaction anabolic or catabolic

A

Anabolic

79
Q

What does a phase 2 reaction involve

A

Conjugation to produce more inactive compounds

80
Q

Example of a microsomal enxxyme found in the liver

A

Cytochrome P450s
Alcohol dehydrogenase
MAO

81
Q

What must happen in the liver in order for the drug to be metabolised

A

It must cross the plasma membrane

82
Q

What are prodrugs

A

Drugs which only become active once they have been metabolised

83
Q

What two things govern the rate of enzymatic metabolism

A

Ammount of enzyme

The max rate the enzymes are able to function at

84
Q

Increasing the ammount of enzyme present is known as

A

Induction

85
Q

What is the knock on effect of adding more enzyme - how would this effect a second dose

A

Drug is being broken down more efficiently so a dose of the same concentration would have a decreased effect

86
Q

If the drug is able to combine with bile what is avoided

A

Metabolism

87
Q

What reactions occur during the phase one reaction of aspirin

A 
Oxidation 
Hydroxylation
Dealkylation 
Deamination 
Hydrolysis
88
Q

State the 3 types of products in the elimination of aspirin

A

Drug
Derivative
Conjugate

89
Q

State the 3 products in the elimination of aspirin

A

Aspirin
Salicylic acid
Glucuronide

90
Q

What is the type of reaction aspirin occurs during its phase II reaction

A

Conjugation

91
Q

Why is paracetamol toxic when overdose taken

A

During phase I reaction a highly toxic product to the liver is produced

92
Q

Over how many genes for cytochrome p450 enzymes

A

Over 57

93
Q

What are the individual variations in P450 enzymes

A

Single nucleotide polymorphisms

94
Q

What is the effect of different isoforms of P450 enzymes

A

They react with different drugs

95
Q

IA2 is a

A

Inducer of P450 drug metabolism

96
Q

3 examples of IA2

A

Brocoli
Brussel sprouts
Tobacco

97
Q

Glomerular filtration will remove drugs with a

A

Low Mr

98
Q

Will drugs bound to albumin be filtered

A

No - Mr of 68’000

99
Q

What is active tubular secretion

A

Transport of drugs directly into the urine

100
Q

How do liophilic molecules get excreted

A

Passive diffusion across the plasma membrane

101
Q

Describe how penicillin is cleared

A

Cleared on a single pass

102
Q

Describe how diazepan is cleared from the body

A

Cleared very slowly

103
Q

What are two other methods for elimination of drugs

A

GI excretion - bound up by food

Expired by the lungs

104
Q

Time course of clearance follows what

A

A mono exponential decay

105
Q

Time course of clearance is determined by

A

Metabolism and excretion

106
Q

Is half life always constant for the same drug

A

Yes

107
Q

What is half life

A

Time taken for the concentration of drug to fall by half

BMS242 Core Phys Pharm (9 decks)

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