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BRS2 > Principles of Pharmacology > Flashcards

Principles of Pharmacology Flashcards

1
Q

What is PHARMACOLOGY?

A

The way in which a drug interacts with a living organism and how this affects physiological action

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2
Q

What is pharmacodynamics?

A

what effect the drug exerts on the body:
where is the effect produced?
what is the drug’s target?
what response is produced after interaction with the drug?

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3
Q

Vast majority of drug targets are proteins: proteins can be further split into 4 subcategories, what are these?

A

ion channels
transport proteins
enzymes
receptors

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4
Q

What is the drug target for ASPIRIN?

A

‘ENZYME’ - cyclooxgenase, bocks the production of prostaglandins

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5
Q

What is the drug target for local anesthesia?

A

Na+ channels- as this stops nerve conduction in that area

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6
Q

What is the drug target for nicotine?

A

the nicotinic acetycholine receptor - nicotine binds to this and activates it

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7
Q

What is the drug target for prozac ( an antidepressant)?

A
  • prozac is a serotonin reuptake inhibitor so it BLOCKS serotonin carrier proteins and prevents serotonin being returned to the synapse
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8
Q

What are the 2 possible effects a drug can have on a target?

A
  • stimulate an effect (e.g nicotine acting on nACh receptors) OR block an effect from being produced
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9
Q

Drugs require SELECTIVITY (speificity) so they only interact with the desired target. In the body, certain molecules have similar structures, give an example:

A

dopamine, serotonin and noradrenaline all have a benzene ring with at least one hydroxyl group attached (2 in the case of dopamine and noradrenaline)

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10
Q

How is drug dose determined?

A

If we know that a drug is 50x more selective for target A than it is for target B, we start at a low dose and increase until we start to see an effect at target A (we now know that to see an effect at target B, we will need 50x the dose needed at target A)

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11
Q

What can happen if a drug is not really specific and can bind to various unwanted targets?

A

SIDE effects

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12
Q

Why is it difficult to determine how much of the drug will actually reach the target?

A

due to the complex way in which the body handles the drug (pharmacokinetics)

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13
Q

Drugs can interact with RECEPTORS through a variety of chemical reactions, name 4 of these? (EHCS)

A

ELECTROSTATIC interactions - MOST common, involve Van der Waals forces and hydrogen bonds

HYDROPHOBIC - important for lipid soluble drugs

COVALENT - least common as reactions tend to be irreversible

STEREOSPECIFIC - many drugs exists as stereoisomers and interact stereospecifically with receptors

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14
Q

In terms of drug interactions with receptors, drugs can be split into agonists and antagonists. What do agonists do?

A

agonists bind to the receptor and ACTIVATE it

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15
Q

In terms of drug interactions with receptors, drugs can be split into agonists and antagonists. What do ANTAGONISTS do?

A

ANTAGONISTS bind to receptors and jam them/ stop the mechanism from working :

e.g V2 receptor ANTAGONIST Vaptan = expensive drug used in treatment of Syndrome of Inappropriate ADH, it binds to V2 recpetor and stops the binding of ADH to V2 –> water reabsorption is reduced

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16
Q

2 key properties for agonists are affinity and efficacy. What does affinity mean?

A

Having a greater affinity means that the drug forms strong drug- receptor complexes > so at any given time, is more likely to be bound to a receptor

NB: individual drug-receptor interactions are transient meaning that with many interactions only lasting milliseconds. If you were to focus on one individual drug molecule amongst the many thousands that might be present, then at any given moment that particular drug molecule might be bound to a receptor, or it may have unbound and may currently be free with the potential to bind another receptor.

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17
Q

In terms of agonists: what does EFFICACY mean?

A

The ability of the drug to produce an effect once bound to the receptor

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18
Q

In terms of efficacy (level of effect produced when bound to the receptor), what are the 3 types of agonists?

A

ANTAGONIST - has affinity for the receptor but NO EFFICACY, therefore acts as a receptor antagonist. When bound to the receptor, it is effectively ‘blocking’ that receptor and preventing an agonist from binding to the receptor and inducing activation.

PARTIAL AGONIST: has affinity for the receptor and SUB-MAXIMAL EFFICACY. It therefore acts as a partial agonist. When bound to the receptor, it can produce a partial response, but cannot induce the maximal response from that receptor.

FULL AGONIST- has affinity for the receptor and MAXIMAL EFFICACY It therefore acts as a full agonist. When bound to the receptor, it can produce the maximal response expected from that receptor.

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19
Q

What is POTENCY?

A

The CONCENTRATION/ DOSE of a drug required to produce a DEFINED effect

(is a bit vague so standard measure of potency = concentration or dose of a drug required to produce a 50% tissue response)

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20
Q

What is the standard measure of potency?

A

The dose/ conc. of a drug required to produce a 50% tissue response

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21
Q

What is the standard nomenclature for concentration or dose of a drug required to produce a 50% tissue response (a.k.a the standard measure of potency)

A 
EC50 = half maximal effective CONCENTRATION 
ED50 = half maximal effective DOSE
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22
Q

The HIGHER the ED50 or EC50 of a drug, the …….. POTENT the drug is

A

LESS - because it means you need more of the drug to illicit the same effect

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23
Q

What is pharmacokinetics?

A

A study of how the BODY deals with the drug (i.e absorption, distribution, metabolism and excretion)

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24
Q

What does pharmacokinetics determine in terms of drug usage?

A

HOW MUCH of the drug will actually reach the target tissue

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25
Q

What are the 4 major pharmacokinetic factors? (ADME)

A
  • absorption
  • distribution
  • metabolism
  • excretion
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26
Q

With regard to pharmacokinetics,how would you define absorption?

A

the passage of the drug FROM site of administration INTO plasma

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27
Q

An important factor that is linked to absorption when talking about pharmacokinetics is BIOAVAILABILITY. Define this.

A

The fraction of the INITIAL drug dose that gains access to the SYSTEMIC circulation

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28
Q

For a drug adminstered via intravenous injection, what would the bioavailability for this drug?

A

100% because ALL of the drug has access to the systemic circulation as it is injected straight into the blood.

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29
Q

Give 4 examples of how drugs can be administered?

A
  • dermal (percutaneously)
  • intra-nasally
  • orally
  • inhalationally
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30
Q

Give the 2 methods by which drug molecules move around the body?

A
  • Bulk flow transfer (i.e in bloodstream, from ana area of HIGH pressure to lower pressure)
  • Diffusional transfer (molecule buy molecule across short distances)
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31
Q

Why is the bioavailability likely to be lower than 100% for intranasal, oral, dermal and inhalational drugs?

A
  • because they move by diffusion, across at least one lipid membrane
32
Q

What is PINOcytosis?

A

when a small part of the cell membrane envelops a molecule, forming a vesicle containing the molecule . e vesicle can then release the chemical on the other side of the membrane.

33
Q

What are the 2 major ways in which drugs across membranes?

A
  • carrier -mediated transport

- diffusion across lipid membranes (NB: drugs have to be lipid soluble to do this)

34
Q

Why is it that diffusion across aqueous pores/ channels is NOT used by drugs to get across membranes?

A

Most pores are less than 0.5nm in diameter, and since there are very few drugs this small, there is little movement of drugs across this aqueous route.

35
Q

Most drugs are either weak acids or weak bases. What 2 forms do these exist in?

A

Ionised and UNionised

36
Q

In the Unionised form, the drug reatins more lipid solubility. True or false?

A

True

37
Q

Whether or not adrug becomes ionised or not depends on what TWO factors?

A
  • DISSOCIATION CONSTANT (pKa) of the DRUG

- pH in that PARTICULAR PART OF THE BODY

38
Q

When the pKa of the drug and the pH of the tissue are equal, the drug will be …..

A

EQUALLY DISSOCIATED BETWEEN ITS 2 forms: 50% ionised, 50% unionised (is the same for drugs that are weak acids or weak bases)

39
Q

For drugs that are weak acids, like aspirin, as the pH of the tissue decreases (i.e H+ conc. is increasing), what form dominates?

A

The UNionised form of the drug dominates (as there are a lot of H+ ions in surrounding tissue, drug does not need to donate its own)

40
Q

For drugs that are weak bases (+accept protons), as the pH decreases, what form of the drug dominates?

A

the IONISED form of the drug begins to dominate

41
Q

In what state: ionised OR unionised is it easier for drugs to cross a membrane?

A

UNionised as they are more lipid soluble in this form

42
Q

Give examples of areas in the body with a higher pH

A

urine and blood

43
Q

Give an example of a place in the body that has a very low pH?

A

the stomach

44
Q

Once a drug has been absorbed, it needs to be distributed to the target tissues. What 4 factors influence distribution to tissues?

A
  • regional blood flow
  • plasma protein binding
  • capillary permeability
  • tissue localisation
45
Q

How does regional blood flow affect drug distribution to diff. tissues?

A
  • tissues that receive more blood flow will receive more drug

at rest: liver receives 27% of cardiac output , kidneys 22%, muscles 20%, brain 14% and heart 4%

NB; diff. activities can change amount of blood going to diff. tissues, e.g muscles receive more blood during exercise BUT after large meal, more blood to stomach and intestines

46
Q

What types of drugs is ALBUMIN good at binding to ?

A

ACIDIC drugs

47
Q

What 3 factors affect the amount of a drug that is bound to plasma proteins?

A
  • the free drug concentration
  • the affinity of the drug for the protein binding sites
  • plasma protein concentration

NB: IMPORTANT – Only free drug is available to diffuse out of the blood and access tissues. Any drug that is bound to plasma proteins CANNOT leave the blood until it dissociates from the protein.



48
Q

How many binding sites does the albumin protein have and what does this mean for its binding capacity?

A

albumin has 2 binding sites

- so its binding capacity = conc. of albumin in blood x 2

49
Q

What are the 3 possible structures capillaries can have?

A

continuous - with water-filled GAP junctions and basement membrane is continuous and intact

fenestrated- gaps in endothelium allow substances <80nm to move through + basement membrane is continuous and intact

DISconitinuous - particularly leaky, larger gaps between endothelial cells, basement membrane also has pores

50
Q

What is the structure of the capillaries that make up the BBB (blood brain barrier)?

A

continuous capillaries, with the addition of tight junctions as opposed to the H20-filled gap junctions

51
Q

What type of capillary is it EASIEST for a drug to diffuse out of and into tissues?

A

FENESTRATED capillaries, like those in the LIVER

52
Q

How do drugs diffuse out of the capillaries that make up the BBB and into the brain?

A
  • the use of carrier proteins is the ONLY way as there are no gap junctions (=h20 filled junctions) or pores
53
Q

What type of drugs would find it easy to diffuse out of continuous capillaries?

A

lipid soluble drugs

54
Q

The fenestrations in fenestrated capillaries allow for the movement of what type of molecules?

A

molecules with small molecular weight, including some drugs

55
Q

How does tissue localisation affect drug distribution?

A

see notes on google doc

56
Q

What is the active component in cannabis?

A

delta9 -THC (detla9-tetrahyrdrocannabinol)

57
Q

The process of metabolism of a drug requires the drug to be converted into a metabolite that is as water soluble as possible, why?

A

to make it easier to excrete

58
Q

The major metabolic tissue is the LIVER, what enzymes in the liver are responsible for drug metabolism?

A

mainly cytochrome p450 enzymes

59
Q

Drug metabolism involves two kinds of biochemical reactions, what are these?

A

Phase 1 -main aim = introduce some sort of REACTIVE GROUP to the drug
Phase 2 - main aim is to add a conjugate group to the reactive group

60
Q

What is the purpose of the 2 biochemical reactions (phases 1+2) involved in drug metabolism ?

A
  • reducing the lipid solubility of the drugs which aids excretion and elimination
61
Q

What kind of chemical reactions are involved in phase 1 of drug metabolism (= the addition of a reactive group, i,.e polar groups like nucleophiles and electrophiles)

A
  • oxidation (most common but requires an initial hydroxylation using cytochrome P450 system)
  • reduction
  • hydrolysis
62
Q

Phase 1 metabolic reactions most likely result in the incorporation of what functional groups?

A
  • NH2
  • SH
  • COOH
  • OH
63
Q

Phase 1 of drug metabolism often forms pharmacologically active drug metabolites.In some instances, the parent drug has no activity of its own, and will only produce an effect once it has been metabolized to the respective metabolit. What are these drugs in which the parent drug is inactive, known as?

A

PRO- DRUGS

64
Q

What causes liver damage due to paracetamol overdose?

A

a metabolite of paracetamol and NOT paracetamol itself

65
Q

Phase 2 of drug metabolism aims to add a functional group to the reactive group. What enzymes are largely involved in this?

A

TRANSFERASES - transferring group onto phase 1 metabolite

66
Q

What are the 2 MAIN routes fro drug excretion?

A

through URINE (kidneys) and through BILE (liver)

67
Q

What are the 3 major routes for kidney secretion of drugs?

A
  • glomerular filtration
  • Active tubular secretion (or reabsorption)
  • Passive diffusion across tubular epithelium
68
Q

What kinds of drugs are filtered into the glomerular filtrate?

A

drug molecules with molecular weight LESS than 20,000- meaning they have an additional route for excretion and so should have a HIGHER EXCRETION RATE

69
Q

What kinds of drugs are actively transported INTO the proximal tubules from the blood supply?

A
  • active transporters on PCT for acidic drugs (can move acidic drugs against a conc. gradient)
  • active transporters for basic drugs exists in PCT (transport basic rugs against conc. gradient, into tubules)
70
Q

True or false: active tubular secretion is the most important method of drug excretion from the kidneys

A

true

71
Q

Passive diffusion means that drugs that are more lipid soluble will be reabsorbed into the bloodstream. How will this affect the excretion rate of these drugs?

A

Will be slower as they stay in the body longer

72
Q

What 2 factors affect whether or not a drug will be reabsorbed into the blood from the kidney tubule?

A
  1. Drug metabolism – phase 2 metabolites tend to be considerably more water soluble than the parent drug and are therefore less well reabsorbed.
  2. Urine pH – this can vary from 4.5-8. Based on the pH partition hypothesis mentioned previously, acidic drugs will be better reabsorbed at lower pH (because acidic drugs will assume non-ionic from which is lipid soluble) and basic drugs will be better reabsorbed at higher pH.



73
Q

What type of phase 2 metabolites is the liver particularly good at excreting into bile?

A

phase 2 glucuronide metabolites

74
Q

Which system: the kidneys or the liver, is responsible for most drug excretion?

A

the kidneys (urine)

75
Q

What is enterohepatic recycling and HOW can it cause the effect of a drug to be prolonged?

A

e.g phase 2 glucuronide metabolite transported into bile, excreted into small intestine and then oxidised by gut bacteria, RELEASING glucuronide group –> metabolite is now more lipid soluble —> greater reabsorption from small intestine back into the hepatic portal blood system for return to the liver—> molecule returns to the liver where a proportion will be re-metabolised, but a proportion may escape into the systemic circulation to continue to have effects on the body.

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