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OV3017 Eye Disease > 1 - General Principles of Pharmacology > Flashcards

1 - General Principles of Pharmacology Flashcards

1
Q

what is pharmaoclogy

A

study of drugs

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2
Q

phamacodynamics

A

study of biochemical and physiological effects of drugs on the body
- what the drug does to the body

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3
Q

what is drug: target interaction

A

drugs exert their effect by binding to specific target protein molecules

targets; receptors/enzymes/ion channels.

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4
Q

what is an agonist drug

A

drug can stimulate its target to produce a desired response

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5
Q

what is an antagonist drug

A

drug blocks the target to prevent binding of the natural agonist

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6
Q

sources of drug can be

A
  • natural, e.g alkaloids (Atropine)
  • semi- synthetic (prepared by chemical modification of natural drugs) e.g cyclopentalate
  • synthetic - prepared by chemical synthesis in labs
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7
Q

drugs should have high specificity. what happens if you increase the dose of drug

A

it can cause the drug to affect targets other than the principle ones, which can lead to side effects

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8
Q

the lower the potency of the drug…

A

higher dose needed, greater risk of unwanted effects

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9
Q

what is therepeutic index

A

A measure of the potential of a drug to cause harm
Expressed as a ratio - between the toxic dose and the therepeutic dose of the drug

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10
Q

narrow TI means

A

the drug needs to be prescirbed ore carefully as its more harmful

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11
Q

What is pharmacokinetics

A

study of the absorption, distribution, metabolism/biotransformation and excretion of drug
-what the body does to the drug

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12
Q

Pharmacokinetics examples

A
  • absorbtion
  • distribution
  • biotransformation
  • excretion
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13
Q

most common route of drug entry

A

oral

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14
Q

alternative drug entry routes

A
  • injection (perenteral) non oral
  • local administration (creams/inhaled drugs)
    -intrathecal - inject into spine
    drug ends up in plasma, then sent to target to exhibit response
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15
Q

when are drugs administered by injection

A

if drug needs to be absorbed more rapidly or if poorly absorbed from gut/GI irritation

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16
Q

most common route of excretion

A

kidney (urine)

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17
Q

Absorbtion - elaborate

A

for a drug to reach target tissue, it needs to be absorbed from site of administration

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18
Q

what do unionised (non-polar) drugs do

A

readily penetrate cell membranes as they are lipophillic

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19
Q

most drugs are

A

weak acids or weak bases - can exist in ionised or unionsed forms

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20
Q

what is the balance between ionised/unionised forms determined by?

A

surrounding pH and the dissociation constant PK

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21
Q

pK of drug

A

represents the pH at which the drug is 50% ionised

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22
Q

acid is

A

proton donor

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23
Q

weak acid proton donor equation (henderson-hasselbatch)

A

50% of the drug is in A- (ionised) form
50% of drug is in HA- (non ionised form)

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24
Q

what does position of equilibrium depend on

A

pH

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25
Q

where will the reaction shift in an acid environement

A

left (unionised form)

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26
Q

where will the reaction shift in an alkaline environement for a weak acid

A

to the right (ionised form)

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27
Q

oral absorption process (acid_

A
  1. passes into stomach (acid environment, low pH)
  2. passes through SI, (alkaline, pH of SI rises)

acid environment, H concentration is high, equib shifts to left, so most of drug is un- ionised form: more readily absorbed

28
Q

where are weak acids well absorbed

A

in an acid environemnt ( more readily absorbed in lining of stomach )

29
Q

what happens when drug passes through intestine

A

pH starts to rise in intestine, equib shifts to right, and more of drug is in ionised form (A-).

these molecules are more readily absorbed across membrane . drug has weak absorbtion in alkaline environment

30
Q

where will an acid be concentrated (and less well absorbed)

A

in a compartment with high pH

31
Q

in the intestine when equilibrium if shifted to right, what happens

A

the drug is trapped in ionised form (pH)- the absorption is weaker as the pH is higher

32
Q

ionised form of weak base

A

BH+

33
Q

non ionised form of weak base

A

B

34
Q

weak base degree of ionisation formula

A
35
Q

weak base in acid environment

A

high h+ conc, pH shifts to left.
drug present in ionised form (BH+)

36
Q

describe the weak base in the acid environment

A
  • concentrated
  • low pH
  • not absorbed in this environment
  • drug is trappd in acid enviorment
37
Q

weak base in alkaline environment

A

drug at SI, equib. shifts to right so more of the drug is in un-ionised form (B)

38
Q

describe the weak base in alkaline environment

A

basic drug, non ionised form
-readily absorbed
- greater ability to cross lipid membranes

an alkaline drug will be concentrated in a compartment with low pH

39
Q

where is a weak acid such as aspirin more likely to be absorbed
pKa = 3.5

A

more likley to be absorbed from the stomach (Acid environment)

40
Q

where is a weak base more likely to be absorbed
Pethidin pKa = 8.6

A

In the SI, alkaline enviornment

41
Q

Weak acids more likely to be absorbed where?

A

stomach. found in un-ionsed form. more readily absorbed

42
Q

weak base more likely to be absorbed where>

A

high pk, small intestine. ionised fom

43
Q

what do low and high pK mean

A

low pk - strong acid
high pk - strong base

44
Q

weak acids and bases are well absorbed

A

strong acids (pk <3) and strong base (pk >10) are poorly absorbed since fullty ionised

45
Q

75% of an orally administered drug is absorbed within

A

1-3 hours

46
Q

factors affecting absorbtion

A
  1. gut motility (how rapidly drug moves in gut)
  2. splanchic blood flow
  3. drug formulation
  4. physiochemical factors
47
Q

drug taken after meal?

A

slowly absorbed since progress to SI is delayed

48
Q

how can a drug be formulated to delay absoroption

A
  • special coating around it
  • capsules
  • tablets with resistant coatings
49
Q

what is bioavailibilty

A

(once drug is absorbed) the fraction of the dose that proceeds unaltered from the site of administration and becomes available at the sight of action

50
Q

what is bioavailibility dependant on

A
  • rate of absorbtion
  • first pass metabolism (oral)
51
Q

first pass metabolism

A

the breakdown of a drug by biotransformation by enzymes within the gut wall/liver- before reaches the plasma compartment

52
Q

explains why GTN (angina) effective sublingually but not when swallowed

A
  • if this drug was given orally, would be broken down by 1st pass metabolism.
  • to stop this its given sublingually so absorbtion takes place by oral mucosa - can directly enter into vascular system into plasma
53
Q

following absorption, distribution of drug is not uniform due to

A
  • physiochemical properties of the drug
  • differences in blood flow between tissues (tissues with greater vascular supply will get > proportion of drug)
  • degree of leakiness of the blood vessels within a particular tissue
  • drug may have affinity for a certain tissue e.g melanin or fat
    cyclopentalate high affinity for melanin px (drug takes longer to work in dark iris)
  • plasma protein binding
54
Q

what is plasma protein binding

A

drugs travel in plasma - partly in solution (unbound) or to plasma proteins (bound.
* albumin - acidic drugs/non-steroidal/anti-inflammatory

  • b globin and a acid bind to basic drugs

protein binding reduces availibilty of the active form of the drug.

55
Q

what do protein bound drugs show

A

a restricted tissue distribution + slow elimination

56
Q

how does elimination of drugs occur

A

metabolism (biotransformation) + excretion

57
Q

what does metabolism involve

A
  • the enzymatic conversion of the drug into another chemical entity
58
Q

polar compounds are excreted

A

well

59
Q

non polar compounds are excreted

A

poorly, as excreted by kidney. tend to get reabsorbed across kidney tubules.

metabolism is important for elimination of non polar compounds

60
Q

where does drug metabolism occur

A

mostly takes place in the liver.
purpose is to make the drug more ionised (polar) to hasten secretion by kidneys

61
Q

drug metabolism - 2 types of chemical transformations called

A

phase I
phase II reactions

62
Q

what is the purpose of metabolism

A

to make the drug more polar (hydrophillic) to hasten its secretion by the kidneys

63
Q

what is the phase 1 reaction of metabolism

A
  • adding or unmasking a functional group
  • e.g -OH, NH2, -SH
  • oxidations most common reaction, carried out by cytochrome p450 (CYP)
64
Q

what is the phase 2 reaction of metabolism (conjugation)

A
  • attatchment of a subsituent group (methy, acetyl)
  • these reactions make drug more polar so it can be more readily excreted by kidneys
65
Q

excretion - how do drugs leave the body

A

-mostly in urine (unchanged or polar metabolites)
- secreted in bile via liver, loss of drug via faeces

66
Q

variables affecting drug metabolism

A
  • some drugs increase/inhibit drug metabolising enzymes
  • genetic polymorphisms lead to inter-individual variation in drug metabolism
  • age
66
Q

how does age affect drug metabolism

A
  • neonates have immature drug metabolizing mechanism.
  • elderly have impaired hepatic metabolism of drugs and also show an impaired glomerular filtration rate reducing renal clearance

OV3017 Eye Disease (19 decks)

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