Pharmacodynamics

Question 1

Drug-receptor interaction model

Answer 1

Describes a receptor as being in a state of equilibrium between its inactive form (Ri) and active (Ra) form

Question 2

What is agonist and antagonist

Answer 2

Agonist - activator
Antagonist - inhibitor (drugs that bind to a receptor and prevents activation)

Question 3

Full agonist

Answer 3

High affinity for the receptor when in its active state only

Question 4

Partial agonist

Answer 4

Produce a lower response at full receptor occupancy than do full agonist –> Emax decreased

Question 5

(Conventional) antagonist

Answer 5

Have equal affinity for the receptor in its active and inactive states, so they encourage the receptor to act exactly as it would in the absence of any bound ligand

Question 6

Inverse agonist

Answer 6

Have a greater affinity for the receptor in an in active state, resulting in the receptor spending even more time than it otherwise would in its in active state (eg BDZ acting allosterically on GABA-A receptors to reduce CT flow through this receptor complex)

Question 7

What are receptors and its effect on drugs?

Answer 7

Receptors are component of a cell or organism that interacts with a drug and initiates the chain of events leading to the drug’s observed effects. Because they:
1. Determine dose-response relationship
2. Result in selectivity of drug action
3. Mediate drug effects (both therapeutic and toxic)

Question 8

Describe the dose-response curve

Answer 8

The relation between concentration and effect which is described by a hyperbolic curve

Question 9

Receptor-effector coupling

Answer 9

The link between a receptor and the actual pharmacological response

Question 10

What is spare receptors

Answer 10

Available receptors even when the agonist has elicited a maximal response.
- When spare receptors are available, adding a competitive antagonist (in the presence of an agonist) will have no effect until ALL receptors, including those that were previously spare, are bound.

Question 11

What is Emax

Answer 11

Maximum response that can be produced by the drug

Question 12

Competitive antagonist

Answer 12

With fixed presence of agonist and increasing dose of antagonist –> progressive inhibition of the agonist
- High antagonist concentrations prevent agonist response completely
- High concentration of agonist can completely surmount the effect of a given concentration of antagonist = Emax remains same (agonist concentration effect curve shift right)
- Eg: naloxone vs opioids

Question 13

Irreversible antagonist (non-competitive antagonist)

Answer 13

Receptor antagonist that binds to the receptor in a functionally irreversible fashion –> receptors unavailable to the agonist –> Emax decreased
- Eg: phenoxybenzamine (a-adrenoreceptor antagonist)

Question 14

Chemical antagonist

Answer 14

Antagonist by which one drug makes another drug unavailable for receptor binding by rendering it chemically inactive
- Eg: protamine ionically binds heparin

Question 15

Physiologic antagonist

Answer 15

An antagonist effect that is mediated through an unrelated pathway
- Eg: glucocorticoids increasing BSL in opposition to insulin