Pharmacodynamics

Question 1

What is pharmacodynamics

Answer 1

The mechanism of action for a drug

“How a drug works”

Question 2

Receptor Mechanisms-Cell Membrane Protein Receptors

Answer 2

Imagine a receptor extending out from the cell where a dug can attach to it

Question 3

Receptor Mechanisms-G Proteins

Answer 3

There are many different kinds of G-protein receptors (E.g. Alpha1, Alpha2, Beta1, Beta2, etc)

Question 4

Receptor Mechanisms-Ion Channels

Answer 4

When ion channels are activated by a drug, they open or close specific channels

Question 5

Receptor Mechanisms-Intracellular Receptors

Answer 5

These types of receptors are located inside the cell, so drugs need to bypass the lipid cell wall to reach them

This means drugs wanting to activating these receptors must be lipid soluble

Once a drug has bound it usually leads to a chain of intracellular responses

Ex. Steroids

Question 6

Affinity

Answer 6

Affinity: Tendency of a drug to combine with a receptor

E.g. High affinity means high drug-receptor attachment rate

Question 7

Efficacy

Answer 7

Efficacy: The ability of a drug to initiate the normal cellular effect

E.g. High efficacy means when the receptor binds, is causes a strong cellular response

Question 8

Agonist

Answer 8

Agonist: A drug that when it binds it causes a normal cell response

Agonist drugs mimic natural agonist within the body, binding to receptor to create the same effect but often with a much more significant physiological response

Question 9

Natural Agonist

Answer 9

Natural Agonist are substances within the body that have evolved to produce a response when they bind to an switch on a receptor

Question 10

Antagonist

Answer 10

Antagonist: A drug that when it binds it causes no normal cell response

Work by binding to a cell receptor and blocking access to the receptor from agonists in the body

Can block access to a receptor from natural agonist

Sometimes called blockers

Because antagonists simply block access to a receptor they can also stop the effects of external agonists such as opiates for addiction treatment

Question 11

Full or Partial Agonists and Antagonists

Answer 11

Full causes a maximum response

Partial causes a sub-maximal response

Question 12

Competitive Antagonism

Answer 12

The drug ‘competes’ for the same site as a natural transmitter, effectively blocking the site from any other transmitter

Question 13

Functional Antagonism

Answer 13

The drug produces the opposite effect, effectively (functionally) negating any overall effect

Question 14

Direct Acting Agents

Answer 14

Drugs that are structurally the same as the natural transmitter, and directly attach to the receptor

Question 15

Indirect Acting Agents

Answer 15

Drugs that mimic the natural transmitters effect, but do not directly attach to the same receptor.
They instead act on a secondary site which in turn actives the receptors

Question 16

Potency and ED50

Answer 16

ED50 refers to the amount of drug(a dose) that produces 50% of the maximal effect

Potency is inversely related to ED50

In other words, the lower the amount of drug needed to cause 50% of the maximum effect, the more potent it is

Question 17

• Lethal Dose(LD50)

Answer 17

The dose of drug that is lethal in 50% of the population

Question 18

Therapeutic Index (TI)

Answer 18

Therapeutic index compares the LD50 to the ED50

The smaller the therapeutic index (e.g. the closer to 1), the more risky it is to use

Question 19

Synergism

Answer 19

When two drugs use different modes of action, and the combined effects are greater then the sum of their individual effects

Question 20

Additive

Answer 20

When two drugs act on the same receptor and their combined effects are equal to the sum of their individual effects

Question 21

Potentiation

Answer 21

A special case where one drug has no direct effect, but its presence dramatically increases the active of a different drug

Question 22

Hypersensitivity (anaphylaxis):

Answer 22

o An excessive response to a drug relative to normal. Usually allergic or immune regulated

Question 23

Tolerance

Answer 23

A decreasing intensity of response to a drug over

Question 24

Tachyphylaxis

Answer 24

A rapidly decreasing response to a drug

Question 25

General Mechanisms Around Tolerance-Receptor Down Regulation

Answer 25

The body decreases the amount of available receptors for the drug to bind to

Question 26

General Mechanisms Around Tolerance-Increased Elimination

Answer 26

The body increases the amount of enzymes that eliminate the drug, resulting in quicker reversal and loss of effect

Question 27

General Mechanisms Around Tolerance-Intracellular molecular changes

Answer 27

E.g. The binding of a drug causes temporary reduction of enzyme efficiency and receptor affinity