Lecture 37 - General mechanism of drug action

Question 1

what is the receptor theory

Answer 1

lock and key concept
eg. histamine
histamine binds to receptor
-cells in stomach produce more acid - inflammation of mucus membranes

Question 2

how do drugs work by blocking receptors?

Answer 2

antagonist blocks ligand from binding - prevents response

Question 3

adrenergic receptors

Answer 3

speeds up heart rate
constrics arteries - increases bp
Dilates bronchioles

problem - raise blood pressure and increases heart rate

Question 4

types of adrenergic receptors

Answer 4

b1 (Mainly on heart) ,b2 (mainly on bronchioles) and alpha (mainly on BV)

Question 5

side effects of beta blockers

Answer 5

Propranolol blocks ß 1 and ß 2 receptors
makes asthma worse

Selectivity is only relative
atenolol blocks ß 1 more than ß 2
best avoided still in asthma

Question 6

How do NSAID’s work

Answer 6

inhibt formation of prostaglandins responsible for modulating inflammation

inhibit cyclo-oxgenase

Question 7

what are the side effects of NSAID’S

Answer 7

As they inhibit prostaglandins
-prostaglandins reduce acid production and icnrease mucus in stomach, increase blood to kidneys

side effects - peptic ulceration, salt and water retention

Question 8

What is COX-2

Answer 8

an anti-inflammatory drug target
eg. NSAIDS
specific inhibition muscles

Question 9

COX 1 acts where?

Answer 9

stomach

non-specific inhibition

Question 10

ACE inhibitors

Answer 10

inhibit enzymes

prevent conversion of angiotensin 1 to 2.

Question 11

what is the proposed action of anti-depressants on neurotransmitters

Answer 11

action in the nerve synapse

ssri’s cause reuptake and release serotonin

Question 12

Drugs affecting cell transport

Answer 12

Interfering with the movement of ions across cell membranes

eg. calcium anatagonist - nifedipine

Question 13

Local anaesthetics

Answer 13

Local anaesthetics generally have a lipid-soluble hydrophobic aromatic group and a charged, hydrophilic amine group.

The bond between these two groups determines the class of the drug, and may be amide or ester.

amides - eg. lignocaine, bupivacaine, prilocaine

esters. cocaine and amethocaine

Question 14

how do local anaesthetics work

Answer 14

block transmission of nerve impulses between peripheral pain receptors and CNS

prevent neurone action potential - disrupt ion channel function within cell membrane

occur via specific binding of local anaesthetics to sodium channels - hold them in inactive state

Question 15

mode of action of local anaesthetics

Answer 15

diffuse through the lipophilic nerve membrane unionized
Low pH in cell generates ionized form
Ionized LA blocks the channel
Impulses stopped
Slowly returns to normal and impulses return as block ends

Question 16

factors affecting anaesthetic effects

Answer 16

Small diameter nerve fibres are more sensitive to local anaesthetics than larger fibres so pain sensation is blocked more readily than touch and movement.

The action is dose dependent

The action is pH dependent (inflamed tissues are often acidic and resistant to local anaesthetics)

Question 17

Adverse effects of local anaesthetics

Answer 17

block sodium channels in heart - Myocardial depression, vasodilation

affect CNS - restlessness and at high doses - convulsions

addition of adrenaline - constriction of peripheral vessels

Question 18

Effects of local anaesthetics on absorption and distribution

Answer 18

vasodilatory effects at low concentrations
increases systemic absorption

distribution influenced by degree of tissue and plasma protein binding of the drug

more protein bound agent - more duration of action

Question 19

metabolism and excretion of anaesthetics

Answer 19

Esters (except cocaine) are broken down rapidly by plasma esterases to inactive compounds and consequently have a short half life.

Amides are metabolised hepatically by amidases. This is a slower process, hence their half-life is longer and they can accumulate if given in repeated doses or by infusion.

Prilocaine is also metabolised extra-hepatically.

Question 20

Drugs with a non-specific action

Answer 20

Antacids e.g. aluminum hydroxide
neutralise acid in stomach

Emollients
moisturise skin

General anaesthetics
reduce CNS function

Question 21

Mode of action of antimicrobials

Answer 21

Beta Lactam antibiotics e.g. Penicillins
inhibit bacterial cell wall synthesis

Macrolides e.g. erythromycin
inhibit bacterial protein synthesis

Antifungal agents e.g. nystatin
inhibit ergosterole in fungal cell membrane
mammalian cells use cholesterol

Question 22

Mode of action of antihelminthics

Answer 22

Ascaracides for worm infestatione.g. threadworm

Paralyses worm by acting on nervous system
not absorbed