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LCRS Pharma > Drug action > Flashcards

Drug action Flashcards

1
Q

what is a drug?

A

a chemical substance that interacts with a biological system to cause a physiological effect

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2
Q

what are the four drug target sites?

A

1) receptors
2) ion channels
3) transport systems
4) enzymes

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3
Q

how are receptors defined?

A

usually within the cell membrane
by there agonist and antagonist actions

activated by NT or hormones

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4
Q

examples of an agonist and antagonist

A

agonist- ACh

antagonist- Atropine

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5
Q

what are the two types of ion channels?

A

voltage sensitive/gated channels e.g. VGCC

receptor linked e.g. nAChR

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6
Q

examples of drugs that target ion channels?

A 
Local anaesthetics (sodium channels) 
calcium channel blockers
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7
Q

examples of transport systems that can be targeted

A

Na+/K+ ATPase (by cardiac glycosides e.g. digoxin)

NA re-uptake (e.g TCAs) monoamines in general

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8
Q

examples of drugs that target transport systems

A

tricyclic anti-depressants (TCAs)

cardiac glycosides e.g digoxin

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9
Q

what are the types of drug interactions with enzymes?

A

enzyme inhibitors e.g. anticholinesterases

false substrates e.g. methyldopa

prodrugs e.g. choral hydrate–> trichloroethanol

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10
Q

give an example of a drug with non-specific action

A

drugs that aren’t specific to receptors like paracetamol can have unwanted effects

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11
Q

what is the danger with some non specific drugs?

A

they bind tightly to plasma proteins and therefore create a dangerous untapped reservoir of the drug e.g. warfarin

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12
Q

examples of non specific drugs

A

antacids

osmotic purgatives

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13
Q

what is an agonist drug?

A

it is stimulatory and has an effect

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14
Q

what is an antagonist drug?

A

it mimics and blocks but does not have an effect

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15
Q

the 2 types of agonist drugs

A

full agonists

partial agonists- do not produce the full response and can therefore have some antagonist activity

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16
Q

what does potency of a drug depend on?

A

potency- amount of drug needed to produce a given effect

affinity- strength of the binding between drug and receptor
efficacy- the biological effect of the drug in that it causes a conformational change in the receptor

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17
Q

why is selectivity not specificity?

A

drugs may not be specific to the same receptors at a higher concentration

18
Q

what are the 2 types of antagonist?

A

competitive

irreversible

19
Q

what are competitive antagonists?

A

they bind to the same site as the agonists co-administered
they are surmountable
they shift the D-R curve to the right

e. g. atropine
e. g. propranolol

20
Q

what are irreversible antagonists?

A

the bind tightly to the active site or they bind elsewhere
they are insurmountable
e.g. hexamethonium

21
Q

what are the 4 types of antagonism?

A
  • receptor blockade
  • physiological
  • chemical
  • pharmokinetic (drug met by enzymes)
22
Q

what is the receptor blockade and what activity does it show?

A

competitive and irreversible antagonist action

displays user-dependency

e.g. local anaesthetics

23
Q

what is user-dependency?

A

the more active/often used tissue is, the faster the block is absorbed and becomes effective as there is a higher chance of it entering

e.g. LAs

24
Q

what is physiological antagonism?

A

drugs that bind to two or more different receptors to counter the effects of another substance producing different effects on the same tissue

e.g. histamine (dilator) and NA (constrictor) on blood pressure

25
Q

what is chemical antagonism ?

A

interaction in solution to negate the effects of another substance
not bound to receptors

e.g. the use of dimercaprol in heavy metal poisoning to clump them together into non-toxic lumps for excretion

chelating agents
anti-venom

26
Q

what is pharmacokinetic antagonism ?

A

the clinically important form where the antagonist decreases the concentration of the active drug at the site of action

the body itself antagonises the agonists administered

e.g. barbiturates and their effects of reduced absorption , increased metabolism and increased excretion

27
Q

what are the 5 types of drug tolerance?

A
  • pharmacokinetic factors
  • loss of receptors
  • change in receptors
  • exhaustion of mediator stores
  • physiological adaption
28
Q

what are the pharmacokinetic factors leading to drug tolerance?

A

due to increase rate of metabolism
unregulated enzymes so metabolism is quicker
e.g. barbiturates and alcohol

29
Q

what are the reasons for a loss of receptors leading to drug tolerance ?

A

this is due to membrane endocytosis of receptors (down regulation)

there can also be upregulation (e.g. denervation super sensitivity)

e.g. beta adrenoreceptors

30
Q

what sort of change can occur in receptors leading to drug tolerance?

A

conformational change in receptors (may reduce affinity)

e.g. nAChR at the NMJ

31
Q

what drug causes an exhaustion of mediator stores lead to drug tolerance?

A

e.g. amphetamine where the stores of NA that are usually released become exhausted

32
Q

what is physiological adaption ?

A

the body adapts physiologically to the administration of drugs over time
e.g. a drug causes BP to fall can cause RAS to activate in response to raise BP

33
Q

what is drug tolerance?

A

the gradual decrease in responsiveness to repeated administration

34
Q

what are the four receptor families and what are they based on?

A

type 1- ion channel linked R
type 2- GP linked R
type 3- kinase linked R

these are all embedded in membrane

type 4- intracellular steroid type R

based on molecular structure and/or the signal transduction system

35
Q

type 1 receptors (ICLR)

A

e.g. nAChR, GABAa
4 or 5 binding domains in the subunit

acts in milliseconds

36
Q

type 2 receptors (GPLR)

A

e.g. beta-1-adrenoreceptors (cardiac), mAChR

most receptors of the body are this type
7-TM structure

acts in seconds

37
Q

type 3 receptors (KLR)

A

e.g. insulin type growth factor receptor

only one alpha helix subunit

acts in minutes

38
Q

type 4 receptor (ISTR)

A

e.g. oestrogen receptor, thryoid

located intracellularly unlike the other 3 types
no alpha helix subunit
uses zinc fingers
affects DNA transcription

acts in hours

39
Q

what is the difference between an agonist and antagonist?

A

both have high affinities but antagonists have no efficacy i.e. no biological effect

40
Q

what is the role of excipients?

A

added to drug formulations to improve
- chemical and biological stability
- increased acceptability:
improved appearance, flavour, fragrance

41
Q

what are some formulations for drugs?

A
  • aerosols
  • capsule
  • cream
  • liquid
  • syrup
  • powder
  • soluble tablet

some use the same administrative route e.g. capsule and syrup use oral route

LCRS Pharma (32 decks)

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