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brs (phase 1b) > (pharm) intro to pharmacology > Flashcards

(pharm) intro to pharmacology Flashcards

1
Q

what is pharmacology?

A

the study of drug action - how a drug interacts with living organisms and influences physiological function

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2
Q

what is therapeutics?

A

concerned with drug prescribing and treatment of disease

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3
Q

differentiate between pharmacology and therapeutics

A

pharmacology is to do with the drugs whereas therapeutics is to do with the patient

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4
Q

what is pharmacodynamics?

A

study of what the drug does to the body

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5
Q

what is pharmacokinetics?

A

study of what the body does to the drug

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6
Q

differentiate between pharmacodynamics and pharmacokinetics

A

pharmacodynamics studies ‘what the drug does to the body’ and pharmacokinetics studies ‘what the body does to the drug’

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7
Q

if you want to work out how a drug exerts its effects on the body, what questions need to be asked?

A

1 - what effect? (drugs have multiple effects)

2 - where is this effect produced?

3 - what is the target for the drug?

4 - what is the response that is produced after the interaction with this target?

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8
Q

what must happen for a drug to produce a measurable effect?

A

it must bind to a specific target in the body

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9
Q

what are the four drug target proteins?

A

transport proteins
enzymes
receptors
ion channels

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10
Q

what are the two possible effects when drugs act on targets?

A

stimulatory - enhance activation of the target

inhibitory - prevent activation of the target

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11
Q

what happens when drug selectivity is low?

A

can bind to many structurally similar targets and bring about other effects you don’t want (side effects)

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12
Q

why is dose an important consideration when administering drugs?

A

the lower the dose, the more specific the effects of the drug (will interact with only one, desired target)

dose increases, effect becomes less specific (will interact with more targets) = unwanted effects

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13
Q

what are the four types of chemical interaction through which drugs interact with their receptors?

A

hydrophobic interactions (important for lipid-soluble drugs)

electrostatic interactions (van der Waals, hydrogen bonds)

covalent bonds (irreversible)

stereospecific interactions

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14
Q

what is an agonist?

A

a drug that bind to a receptor inducing activation

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15
Q

what is an antagonist?

A

a drug that bind to a receptor preventing activation

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16
Q

define affinity

A

extent to which a drug binds to receptors at any given drug concentration

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17
Q

define efficacy

A

the ability of an individual drug molecule to produce an effect once bound to a receptor

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18
Q

what does affinity determine?

A

the strength of the drug-receptor complex

higher affinity = stronger drug-receptor complex

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19
Q

explain what an full agonist is in terms of affinity and efficacy

A

drug that has affinity for the receptor and maximal efficacy

= maximal response

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20
Q

explain what an receptor antagonist is in terms of affinity and efficacy

A

drug has affinity for receptor BUT no efficacy

= prevents activation by preventing agonist binding

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21
Q

explain what an partial agonist is in terms of affinity and efficacy

A

drug has affinity for the receptor but sub-maximal efficacy

= partial response but cannot induce maximal response

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22
Q

define potency

A

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

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23
Q

differentiate between potency and efficacy

A

potency is the concentration or dose of a drug that is required to produce a desired response HOWEVER
efficacy is the ability of the drug to produce the effect once bound to the receptor

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24
Q

what are the categories of efficacy?

A

full agonists, partial agonists, antagonists

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25
Q

what is the standard measure of potency?

A

EC50 (half maximal effective concentration) = concentration of drug required to produce a 50% tissue response

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26
Q

what is EC50?

A

half maximal effective concentration = concentration of drug that is required to produce a 50% tissue response

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27
Q

what is ED50?

A

half maximal effective dose = dose of drug required to produce desired effect (in 50% of individuals)

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28
Q

differentiate between EC50 and ED50

A

EC50 = hald maximal effective CONCENTRATION but ED50 = half maximal effective DOSE

while EC50 is the concentration of the drug that will produce a 50% tissue response, ED50 is the dose of drug required to produce desired effect (in 50% of individuals tested)

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29
Q

what does it mean if a drug is very potent?

A

very potent = very small amounts of the drug are required to to produce the desired response

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30
Q

what is more potent: a full agonist or a partial agonist?

A

cannot compare potency as full/partial agonist are measures of efficacy

potency is related to dose of drug required to produce response WHEREAS efficacy determines the ability of the drug to produce a desired effect and has nothing to do with concentration/dose

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31
Q

what does it mean if a drug is highly potent?

A

very small amounts of the drug are required to produce a large response

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32
Q

what does it mean if a drug is highly efficacious?

A

the drug can produce a maximal response

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33
Q

what is more important potency or efficacy?

A

efficacy - as the priority is to produce the maximal response

even if potency is low, the dose can be adjusted to a higher one as long as the maximal response is achieved

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34
Q

define absorption

A

the passage of the drug from the site of administration into the plasma

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35
Q

define bioavailability

A

the fraction of the initial dose that gains access to the systemic circulation

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36
Q

differentiate between absorption and bioavailability

A

absorption deals with the process of drug transfer into the systemic circulation however bioavailability refers to the outcome of the drug transfer into the systemic circulation (i.e. how much)

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37
Q

what determines absorption and bioavailability?

A

site of administration

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38
Q

what are the forms of drug administration?

A 
oral
dermal (percutaneous)
inhalation
intranasal
intravenous
intramuscular
39
Q

what are the specific absorption and bioavailability in terms of intravenous drug administration?

A

absorption - process is injecting full dose straight into bloodstream

bioavailability - outcome is as drug injected straight into the systemic circulation = 100% bioavailability

40
Q

what are the two methods that drugs use to move around the body?

A

bulk flow transfer (i.e. in the bloodstream)

diffusional transfer (i.e. molecule by molecule across short distances)

41
Q

what is bulk flow transfer?

A

movement in the bloodstream

42
Q

what is diffusional transfer?

A

molecule by molecule over short distances

43
Q

in terms of the intravenous route, what method of drug transfer is used?

A

bulk flow transfer delivers the drug to the site of action

44
Q

what is the more common method of drug transfer?

A

diffusional transfer

45
Q

what are the four mechanisms by which chemicals can diffuse across plasma membranes?

A

1 - pinocytosis
2 - simple diffusion across membranes (lipid-soluble substances only)
3 - diffusion across aqueous pores
4 - carrier-mediated transport (using transmembrane protein)

46
Q

explain the process of pinocytosis

A

a small part of the cell membrane envelops the chemical molecule and forms a vesicle containing the drug which can be released on the other side

47
Q

explain the process of simple diffusion of drugs

A

lipid-soluble molecules will diffuse across lipid membranes down a concentration gradient

48
Q

what feature must molecules exhibit to take part in simple diffusion?

A

lipid solubility

49
Q

explain the process of drug diffusion using carrier-mediated transport

A

transmembrane proteins will bind drugs on one side and will undergo a configurational shape change that causes movement of the drug to the other side

50
Q

explain the process of drug diffusion across pores

A

uncommon as the are gaps between endothelia/epithelial cells that are usually less than 0.5nm in diameter so won’r fiit drug molecules

51
Q

what are the two main structural types for drugs?

A

weak acid or weak base (so they exist either in the ionised or unionised form)

52
Q

what do weak acids do in their ionised form?

A

donate protons (H+)

53
Q

what do weak bases do in their ionised form?

A

accept protons (H+)

54
Q

which form of the drug is likely to take part in simple diffusion: ionised or unionised? (and why)

A

unionised - as they are more lipid soluble

55
Q

what two factors determine the ionisation status of a drug?

A

the pKa (dissociation constant)

the pH in that particular part of the body

56
Q

what happens when the pKa of the drug and the pH of the tissue is equal?

A

the drug will be equally dissociated between the two forms: 50% ionised, 50% unionised

57
Q

what happens to the ionisation status as the pH changes for weak acids?

A

if pH decreases for weak acids (i.e. become more acidic) = more unionised

if pH increases for weak acids (i.e. become more alkaline) = more ionised

58
Q

what happens to the ionisation status as the pH changes for weak bases?

A

if pH decreases for weak bases (i.e. become more acidic) = more ionised

if pH increases for weak bases (i.e. become more alkaline) = more unionised

59
Q

why is bioavailability likely to be under 100% for most of the routes of drug administration?

A

as most drug transfer occurs via diffusional transfer first rather than bulk flow transfer directly (only intravenous)

60
Q

what determines drug distribution to tissues?

A

regional blood flow, plasma protein binding, capillary permeability, tissue localisation

61
Q

how does regional blood flow determine drug distribution?

A

at rest, different tissues receive different amounts of the cardiac output and therefore different concentrations of the drug

62
Q

when can regional blood flow change?

A

during exercise (more blood diverted to muscles)

after a meal (more blood diverted to GI tract)

63
Q

once in the systemic circulation, what do drugs bind to?

A

plasma proteins (e.g. albumin)

64
Q

what three factors determine how much drug is bound to plasma proteins?

A

concentration of free drug

affinity of drug for plasma protein

concentration of plasma protein

65
Q

what are the four types of capillary structures?

A

continuous (w H2O filled gap junctions)

discontinuous

blood brain barrier (w tight junctions)

fenestrated

66
Q

what is the most common capillary structure?

A

continuous

67
Q

how are lipid-soluble drugs delivered to tissues?

A

simple diffusion across the endothelial cells (i.e. continuous capillaries)

68
Q

how are non-lipid-soluble drugs delivered to tissues?

A

carrier proteins (i.e. blood brain barrier)

69
Q

where can discontinuous capillary structure be found?

A

liver

70
Q

where can fenestrated capillary structure be found?

A

glomerulus of the kidney

71
Q

why does the liver have discontinuous capillaries?

A

to enable the majority of the drugs in the bloodstream to diffuse into the liver tissue and be metabolised

72
Q

why does the glomerulus of the kidney have fenestrated capillaries?

A

to enable small drugs to be excreted more efficiently from the bloodstream

73
Q

explain tissue localisation in terms of drug distribution

A

a lipid soluble drug is more likely to remain in a region with a high fat content (high retention in the brain)

a water soluble drug is more likely to remain in a region with a high water content (i.e. high retention in plasma)

74
Q

in order for a drug to be excreted, what property must it exhibit and why?

A

high levels of water solubility so they remain in the bloodstream and are easier to excrete and elimainate

75
Q

in order for a drug to be excreted, what property must it exhibit and why?

A

high levels of water solubility so they remain in the bloodstream and are easier to excrete and eliminate in urine/bile

76
Q

why is it important to excrete/eliminate drugs from the body?

A

to prevent them from have a continuous, unwanted effect

77
Q

what are the two steps to drug metabolism in the liver?

A

phase 1 metabolism - add a reactive group to the drug

phase 2 metabolism - add a conjugate to the reactive group

78
Q

which enzymes are responsible for phase 1 drug metabolism in the liver?

A

cytochrome p450 enzymes

79
Q

which enzymes are responsible for phase 2 drug metabolism in the liver?

A

transferases

80
Q

what can phase 1 metabolism in the liver sometimes also form?

A

pharmacologically active drug metabolites that can have negative unwanted effects

81
Q

what is first pass (pre-systemic) metabolism?

A

when orally administered drugs are metabolised in the liver prior to enter the systemic circulation = little active drug reaches circulation

82
Q

how can the problem posed by first pass (pre-systemic) metabolism be tackled?

A

administer a larger dose of orally administered drug to ensure sufficient levels of active drug reach the systemic circulation

83
Q

why does pre-systemic metabolism occur?

A

orally administered drugs are absorbed form the small intestine and then travel to the liver via the hepatic portal system

= so can be metabolised before reaching the systemic circulation (little active drug ends up here)

84
Q

what are the main ways drugs can be excreted by the body?

A

via lungs (e.g. alcohol breath test)

via breast milk (in females - careful not to take drugs that can affect baby)

via kidney (in urine)

via liver (in bile)

85
Q

what are the three routes for excretion via the kidney?

A

glomerular filtration (depends on size of drug)

active secretion (acidic and basic drugs secreted using transporters)

passive reabsorption (based on urine pH and extent of drug metabolism - only lipid soluble drugs)

86
Q

explain how glomerular filtration is a method od drug excretion

A

drugs w a molecule weight less than 20,000 can diffuse into the glomerular filtrate

= additional method of excretion so quicker rate of excretion

87
Q

explain how glomerular filtration is a method of drug excretion

A

drugs w a molecule weight less than 20,000 can diffuse into the glomerular filtrate

= additional method of excretion so quicker rate of excretion

88
Q

explain how active tubular secretion is a method of drug excretion

A

drug can be excreted via active transport carrier systems

89
Q

explain how passive diffusion is a method of drug excretion

A

if drugs are particularly lipid soluble, will be reabsorbed from tubule back into the systemic circulation

90
Q

what two factors determine the extent of drug reabsorption via passive reabsorption in the kidney?

A

drug metabolism (water soluble phase 2 metabolism less well reabsorbed)

urine pH (acidic drugs better reabsorbed at lower pH, basic drugs better reabsorbed at higher pH)

91
Q

you are taking Drug A as an analgesic – it is a weak acid

the urine pH suddenly increases from 6.5 to 8

will the drug effect be prolonged or reduced over the next few hours?

A

weak acid + pH increase = more ionised

if more ionised = less lipid soluble so less drug passively reabsorbed in the kidney tubule so more efficient excretion SO drug effect reduced over next few hours

92
Q

describe how biliary excretion is a method of drug excretion

A

drugs transported from plasma into bile via liver cells, excreted into intestines and eliminated in faeces

93
Q

how does enterohepatic recycling prolong drug effect?

A

metabolite is transported into the bile

metabolite is excreted into the small intestine, where it is hydrolysed by gut bacteria releasing the conjugate

loss of the conjugate increases the lipid solubility of the molecule

increased lipid solubility allows for greater reabsorption from small intestine back into the hepatic portal blood system for return to the liver

the molecule returns to the liver where a proportion will be re-metabolised (conjugate re-added), but a proportion may escape into the systemic circulation to continue to have effects on the body

brs (phase 1b) (71 decks)

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