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Yr 2 LCRS - Pharm > 2 - Drug-Receptor Interactions > Flashcards

2 - Drug-Receptor Interactions Flashcards

1
Q

Define Pharmacokinetics

A

“Effect of body on drug”

Concerned with the movement of drugs in the body -

Absorption, Distribution, Metabolism, Excretion

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2
Q

Define Pharmacodynamics

A

“Effect of drug on body”

Concerned with drugs and the mechanism of action

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3
Q

What is the purpose of co-administered drugs?

A

Antagonism

One drug can inhibit the action of another

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4
Q

What are the 4 main drug target site categories?

A

1) Receptors
2) Ion Channels
3) Transport Systems
4) Enzymes

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5
Q

What is the first thing a drug must do when it enters the body?

A

Find its target site

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6
Q

How do drugs target receptors?

A
  • Receptors usually in cell membranes
  • Activated by neurotransmitter or hormone
  • Defined by agonists and antagonists
  • 4 types of receptor
  • Ion channel
  • G-protein linked
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7
Q

What is an agonist?

A

A ligand that stimulates a receptor

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8
Q

What is ACH’s target site and how does it work?

A

Receptor

Non-selective agonist for both muscarinic and nicotinic receptors.

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9
Q

What is atropine’s target site and how does it work?

A

Receptor

Selective antagonist for muscarinic receptors.

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10
Q

What are ion channels and what are the two types?

A

Selective pores which allow ion transfer down electrochemical gradients.

2 TYPES:

1) Voltage sensitive
* e.g. VSCC
2) Receptor Linked/Ligand Gated
* e.g. Nicotinic ACh Receptors nAChRs

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11
Q

How do drugs target ion channels?

A

Calcium Blockers

  • block calcium transfer in smooth muscle
  • used to treat angina, blood pressure, arrthymias

Local Anaesthetics

  • interact with VSSCs
  • reduce sodium influx into cells
  • sensory fibres have less sodium
  • fewer APs to sensory motor cortex
  • less pain perceived
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12
Q

Define the term ‘drug’

A

A chemical substance that interacts with a biological system to produce a physiological effect.

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13
Q

What type of drug target site are the words agonist and antagonist used in relation to?

A

Receptors

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14
Q

What are transport systems?

A

transport systems allow for transport against concentration gradients

e.g. Na+/K+ ATPase, NA ‘uptake 1’

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15
Q

How drugs target transport systems?

A

Tri-Cyclic Antidepressants (TCAs)

  • 3 ring structure
  • interacts with NA ‘uptake 1’
  • bind to NA in brain
  • in depression, NA is not being taken up by receptors but has high reuptake
  • TCAs increase NA time in cleft

Cardiac Glycosides

  • cardiac stimulants
  • good in heart failure
  • increases contractility of heart
  • digoxin increases Na+/K+ ATPase activity on cardiac myocytes
  • changes concentrations
  • increases intracellular Ca2+
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16
Q

How do drugs target enzymes?

A

THREE MAIN METHODS

1) Enzyme inhibitors

  • e.g. anticholinesterases
  • ACh not broken down
  • neostigmine, used in myasthenia gravis

2) False Substrates

  • e.g. used to subvert normal pathway.
  • methyldopa for increasing BP, takes place of DOPA in NA creation, synthesises fake NA called methylNA, doesn’t vasoconstrict as well as NA

3) Prodrugs

  • e.g. needs to interact with enzyme to become activated
  • chloral hydrate for insomnia, becomes tricholorethanol, enzyme needed is in the liver
17
Q

How can enzymes also cause unwanted side effects with regards to drug use?

A

EXAMPLE: Paracetamol

It is metabolised in the liver.

If taken too much, enzymes become saturated.

Therefore, a different enzyme is used for the metabolism.

Unwanted metabolic side effects on liver.

18
Q

What is non-specific drug action?

A

It can’t be classified into the 4 main drug target sites.

Drugs with physiochemical properties.

  • e.g. antacids
  • Aluminium or Magnesium Hydroxides
  • acid + base –> salt + water
  • e.g. osmotic purgatives
  • draw H20 into the gut
  • increase gut activity
  • softens stool
  • increase content of excrement
19
Q

How can drugs interact with plasma proteins?

A

Many drugs bind to plasma proteins (PPB) such as albumin.

The drugs are then inactive until free.

They are not producing a physiological response, just acting as a reservoir.

e.g. Warfarin and Asparin are highly bound

20
Q

Name some examples of agonists

A

ACh

Nicotine

21
Q

Name some examples of antagonists

A

Atropine

Hexamethonium

22
Q

What is the potency of a drug?

A

Potency is a measure of drug activity expressed in terms of the amount required to produce an effect of given intensity.

“The strength of a drug”

23
Q

What does the potency of a drug depend on?

A

Depends on affinity and efficacy

24
Q

Define drug affinity

A

Affinity - How well a drug can bind to a receptor

25
Q

Define drug efficacy

A

Efficacy - The ability of a drug to cause a conformational change in a receptor and generate a response.

It involves a transduction system.

26
Q

What factors make a good agonist?

A

High affinity and efficacy.

27
Q

What is the difference between a full and partial agonist?

A

Partial agonists are drugs that bind to and activate a given receptor, but have only partial efficacy at the receptor relative to a full agonist.

28
Q

Why would you administer a partial agonist with a full agonist?

A

When administered with a full agonist, partial agonists can act as antagonists.

29
Q

Define drug selectivity

A

Selectivity is the degree to which a drug acts on a given site relative to other sites. Relatively nonselective drugs affect many different tissues or organs.

30
Q

What is the structure-activity relationship?

A
  • ‘lock-and-key’
  • the relationship between the chemical or 3D structure of a molecule and its biological activity.
  • change drug structure = change drug’s activity
  • first must fit into lock, then must change activity in lock
31
Q

What kind of curve is present on a log dose-response curve?

A

Sigmoid Curve

  • atraight line upwards mainly
  • analyse shifts to see difference between full and partial agonists
32
Q

How do you label the axes on a dose-response curve?

A

x axis = Agonist concentration [A]

y axis = Tissue Response (over time)

33
Q

What is different between agonists and antagonists with regards to affinity and efficacy?

A

Antagonists have affinity but no efficacy for receptors that they act on.

34
Q

What are the different forms of receptor antagonist?

A

1) COMPETITIVE

  • binds to same site as agonist
  • shifts D-R curve to the right
  • can be overcome by high amounts of agonist
  • surmountable
  • e.g. atropine is a competitive muscarinic co-receptor antagonist
  • e.g. propanolol is a Beta 1 and 2 blocker

2) IRREVERSIBLE

  • binds tightly with covalent bonds or to a different site than the agonist
  • no displacement by agonist
  • insurmountable
  • e.g. hexamethonium is a nACHr blocker
35
Q

What is the exception to the phrase “all receptors are in cell membranes”?

A

Steroid receptors

36
Q

How long until you feel the effects of paracetamol overdose on liver and kidneys?

A

Can be up to 24-48 hours and is irreversible.

37
Q

How do General Anaesthetics have non-specific drug action?

A

They dampen synaptic transmission but they do not interact with a specific transport system or receptor.

38
Q

What is ‘Receptor Reserve’?

A
  • spare receptors
  • in some tissues, you don’t have to occupy 100% of the receptors to generate a maximal response

Yr 2 LCRS - Pharm (44 decks)

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