MR 8 Drugs and Receptors Flashcards Preview

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Flashcards in MR 8 Drugs and Receptors Deck (36):
1

How do drugs exert their effects?

By binding to a target, often protein, occasionally DNA (some antimicrobial and antitumour drugs). Most bind reversibly with receptors, binding governed by association and dissociation rates

2

What can be targets of drugs?

Enzymes, GPCRs, ion channels, transporters, nuclear hormone receptors, other receptors

3

How much is a mole?

6x10^23 particles.

4

What is a molar solution?

Solution containing 1 mole in 1 litre

5

Are drugs of equivalent concentrations by weight, always the same concentration?

No but drugs of equivalent molar concentrations are

6

What are drugs that bind to receptors and cause a response called? What qualities do they have?

Agonists
Both efficacy and affinity

7

What are drugs that bind to receptors but don't cause a response called? What qualities do they have?

Antagonists
Affinity only

8

What is affinity?

Likelihood of a ligand binding to its target

9

What is intrinsic efficacy?

Likelihood of activation

10

How is binding information often obtained?

through binding of a radioligand

11

What is Bmax?

Maximum binding capacity
Gives info about number of receptors

12

What is Kd?

The concentration needed for 50% occupancy
This is a measure of affinity and a lower Kd indicates higher affinity

13

What are concentration response curves used for?

Measuring a response in cells/tissues

14

What are dose response curves used for?

Measuring a response in whole animal

15

What is Emax?

The maximum response

16

What is EC50?

Effective concentration giving 50% of maximal response.
Measure of potency

17

What is potency?

depends on affinity, intrinsic efficacy and efficacy.
Efficacy + affinity= potency

18

What is efficacy?

Likelihood of response

19

If two agonists have identical Emax do they have equal efficacy?

No, may differ in affinity

20

What does salbutamol do and why is salbutamol effective?

beta adrenoagonist used to relax the airway via the b2 receptors there.
There are b1 adrenoceptors in the heart which could be affected by salbutamol but as salbutamol has higher affinity for b2 (kd b1=20um Kd b2=1um), because of its B2 SELECTIVE EFFICACY and because of administration route b1 activation and side effects are limited

21

How are side effects prevented using salmeterol?

(Longer acting than salbutamol)
No selective efficacy
Prevents b1 activation through huge difference in affinity
kd b1=1900nm b2=0.55nm

22

What are spare receptors?

These occur when the maximal 100% response does not need 100% receptor occupancy (Ec50

23

What influences whether there will be spare receptors or not?

transduction system/amplification and properties of tissue

24

How do spare receptors affect sensitivity?

Increase sensitivity allowing responses at low agonist concentrations therefore also affecting potency

25

What is a partial agonist?

Drug that cannot produce a maximal effect even with full receptor occupancy

26

What is the relationship between Kd and EC50 in partial agonists?

Kd=EC50

27

Can partial agonists be more potent than full agonists?

Yes as potency involves both efficacy and affinity

28

Is a partial agonist a partial agonist in all tissues?

No can differ as tissue with more receptor would give more of a response

29

What are the three types of antagonists?

Reversible competitive
Irreversible competitive
Non-competitive

30

How common is reversible competitive antagonism and can it be overcome?

Commonest and most important form in therapeutics
Yes, overcome by high agonist concentration

31

Why will a heroin(morphine-full agonist) addict who then takes (partial agonist)buprenorphine become ill?

Buprenorphine has higher affinity than heroin so occupies the receptors anatgonising the heroin. The buprenorphine is only a partial agonist so doesnt give maximal response so addict feels withdrawal symptoms

32

Give an example of a reversible competitive antagonist

Naloxone- antagonises u-opioid receptors. Used to reverse opioid mediated respiratory depression. Its high affinity means it competes effectively with other opioids like heroin

33

How do reversible competitive antagonists affect a concentration response curve?

Parallel shift to right

34

How do irreversible competitive antagonists affect a concentration response curve?

Parallel shift to right and at high concentrations suppresses maximal response as spare and needed receptors filled by antagonist

35

Give an example of an irreversible competitive antagonist?

Phenoxybenzamine
a1 adrenoceptor blocker used in hypertension episodes in pheochromocytoma (tumour of adrenal gland causing excessive NA secretion and vasoconstriction

36

What is non-competitive antagoniism?

Allosteric binding of an antagonist to a receptor