Chapter 5: Pharmacodynamics

Question 1

Pharmacodynamics

Answer 1

Pharmacodynamics is defined as the study of the biochemical and physiologic effects of drugs on the body and the molecular mechanisms by which those effects are produced.

In short, pharmacodynamics is the study of what drugs do to the body and how they do it.

Question 2

What determines the minimum amount of drug needed to elicit a response

Answer 2

Dose-response relationships

Question 3

Dose-response relationships determine:

Answer 3

1. Dose-response relationships determine the minimum amount of drug needed to elicit a response,
2. the maximum response a drug can elicit,
3. and how much to increase the dosage to produce the desired increase in response.

Question 4

Dose-response curves reveal two characteristic properties of drugs:

Answer 4

1. maximal efficacy and
2. relative potency.

Question 5

Maximal Efficacy

Answer 5

Maximal efficacy is defined as the largest effect that a drug can produce.

Question 6

What is Maximal efficacy indicated by on the dose-response curve?

Answer 6

Maximal efficacy is indicated by the height of the dose-response curve.

Question 7

Relative Potency:

Answer 7

The term potency refers to the amount of drug we must give to elicit an effect.

Question 8

How is Potency indicated on the dose response curve?

Answer 8

Potency is indicated by the relative position of the dose-response curve along the x (dose) axis.

Question 9

What does it mean to say morphine is more potent that meperidine?

Answer 9

Because morphine produces pain relief at lower doses than meperidine, we would say that morphine is more potent than meperidine.

Question 10

A potent drug is one that:

Answer 10

A potent drug is one that produces its effects at low doses.

Question 11

What is a consequence of having greater potency?

Answer 11

the only consequence of having greater potency is that a drug with greater potency can be given in smaller doses.

Question 12

Relationship between Potency and efficacy

Answer 12

It is important to note that the potency of a drug implies nothing about its maximal efficacy! Potency and efficacy are completely independent qualities.

Question 13

The only way drugs can produce their effects is by:

Answer 13

interacting with other chemicals.

Question 14

Receptor

Answer 14

We can define a receptor as any functional macromolecule in a cell to which a drug binds to produce its effects.

Question 15

When a drug binds to a receptor, what does it do?

Answer 15

When a drug binds to a receptor, all that it can do is mimic or block the actions of endogenous regulatory molecules.

Question 16

How does a drug effect physiologic activity when it binds to a receptor?

Answer 16

The drug will either increase or decrease the rate of the physiologic activity normally controlled by that receptor

Question 17

When drugs bind to receptors they can do one of two things:

Answer 17

1. They can either mimic the action of endogenous regulatory molecules
2. They can block the action of endogenous regulatory molecules.

Question 18

Agonists

Answer 18

Drugs that mimic the body’s own regulatory molecules are called agonists.

Question 19

Partial agonists

Answer 19

Like agonists, partial agonists also mimic the actions of endogenous regulatory molecules, but they produce responses of intermediate intensity.

Question 20

Antagonists.

Answer 20

Drugs that block the actions of endogenous regulators are called antagonists.

Question 21

What do agonists do?

Answer 21

Are molecules that activate receptors

Question 22

Examples of agonists

Answer 22

Because neurotransmitters, hormones, and all other endogenous regulators of receptor function activate the receptors to which they bind, all of these compounds are considered agonists.

Question 23

What does a drug do when it acts as an agonist?

Answer 23

When drugs act as agonists, they simply bind to receptors and mimic the actions of the body’s own regulatory molecules.

Question 24

An agonist is a drug that has both _____and ____

Answer 24

1. affinity
2. high intrinsic activity

Question 25

What allows agonist to bind to receptors

Answer 25

Affinity allows the agonist to bind to receptors

Question 26

What gives the agonists the ability to activate receptors?

Answer 26

Affinity allows the agonist to bind to receptors, and intrinsic activity allows the bound agonist to activate or turn on receptor function.

Question 27

Affinity

Answer 27

The term affinity refers to the strength of the attraction between a drug and its receptor.

Question 28

Intrinsic Activity

Answer 28

The term intrinsic activity refers to the ability of a drug to activate receptors.

Question 29

An antagonist is a drug with _____for a receptor but with _________

Answer 29

In terms of the modified occupancy theory, an antagonist is a drug with affinity for a receptor but with no intrinsic activity.

Question 30

____ allows the antagonist to bind to receptors,

Answer 30

Affinity

Question 31

_________ prevents the bound antagonist from causing receptor activation.

Answer 31

but the lack of intrinsic activity prevents the bound antagonist from causing receptor activation.

Question 32

Antagonists produce their effects by

Answer 32

Antagonists produce their effects by preventing the activation of receptors by agonists.

Question 33

Antagonists can produce beneficial effects

Answer 33

1. by blocking the actions of endogenous regulatory molecules or
2. by blocking the actions of drugs.

Question 34

Response to an antagonist is determined by

Answer 34

how much agonist is present.

Question 35

If there is no agonist, what does antagonist do?

Answer 35

Because antagonists act by preventing receptor activation, if there is no agonist present, administration of an antagonist will have no observable effect;

the drug will bind to its receptors, but nothing will happen.

Question 36

If there is agonist, what does antagonist do?

Answer 36

On the other hand, if receptors are undergoing activation by agonists, administration of an antagonist will shut the process down, resulting in an observable response.

Question 37

Antagonists can be subdivided into two major classes:

Answer 37

1.noncompetitive antagonists and

2. competitive antagonists.

Question 38

Most antagonists are:

Answer 38

Competitive

Question 39

How do Noncompetitive (Insurmountable) Antagonists bind to receptors?

Answer 39

Noncompetitive antagonists bind irreversibly to receptors.

Question 40

The effect of irreversible binding by noncompetitive antagonists is:

Answer 40

The effect of irreversible binding is equivalent to reducing the total number of receptors available for activation by an agonist.

Question 41

Because the binding of noncompetitive antagonists is irreversible, what does this mean for inhibition?

Answer 41

Because the binding of noncompetitive antagonists is irreversible, inhibition by these agents cannot be overcome, no matter how much agonist may be available.

Question 42

What does noncompetitive antagonists do to the maximal response that an agonist can elicit?

Answer 42

Noncompetitive antagonists reduce the maximal response that an agonist can elicit.

Question 43

Since noncompetitive antagonists bind irreversibly, what does this mean about their effects?

Answer 43

Although noncompetitive antagonists bind irreversibly, this does not mean that their effects last forever.

Cells are constantly breaking down old receptors and synthesizing new ones.

Consequently, the effects of noncompetitive antagonists wear off as the receptors to which they are bound are replaced.

Question 44

Competitive (Surmountable) Antagonists

Answer 44

Competitive antagonists produce a receptor blockade by competing with agonists for receptor binding.

Question 45

How do Competitive antagonists bind to receptors.

Answer 45

Competitive antagonists bind reversibly to receptors.

Question 46

If an agonist and a competitive antagonist have equal affinity for a particular receptor, which will occupy the receptor?

Answer 46

If an agonist and a competitive antagonist have equal affinity for a particular receptor, then the receptor will be occupied by whichever agent—agonist or antagonist—is present in the highest concentration.

Question 47

Intrinsic Activity of Partial Agonists?

Answer 47

A partial agonist is an agonist that has only moderate intrinsic activity.

Question 48

What happens when the receptors of a cell are continually exposed to an agonist?

Answer 48

When the receptors of a cell are continually exposed to an agonist, the cell usually becomes less responsive.

Question 49

When the receptors of a cell are continually exposed to an agonist, the cell usually becomes less responsive. What is this called?

Answer 49

The cell is said to be desensitized or refractory or to have undergone down-regulation.

Question 50

What does continuous exposure to an antagonist do to a cell?

Answer 50

Continuous exposure to antagonists causes the cell to become hypersensitive (also referred to as supersensitive).

Question 51

One mechanism that can cause hypersensitivity in a cell

Answer 51

One mechanism that can cause hypersensitivity is the synthesis of more receptors.

Question 52

For drugs that don’t act through receptors, how do they act?

Answer 52

Rather, they act through simple physical or chemical interactions with other small molecules.

Question 53

An example of drugs that don’t act through receptors?

Answer 53

Antacids neutralize gastric acidity by direct chemical interaction with stomach acid.

Question 54

The Therapeutic Index is a measure of:

Answer 54

The therapeutic index is a measure of a drug’s safety.

Question 55

The Therapeutic Index is defined as:

Answer 55

Is defined as the ratio of a drug’s LD50 to its ED50.

Question 56

LD50 stand for?

Answer 56

average lethal dose

Question 57

The LD50, or average lethal dose,

Answer 57

Is the dose that is lethal to 50% of the animals treated

Question 58

ED50 stands for

Answer 58

ED50 is an abbreviation for average effective dose

Question 59

Average Effective Dose (ED50):

Answer 59

is defined as the dose that is required to produce a defined therapeutic response in 50% of the population.

Question 60

A large (high or wide) therapeutic index indicates

Answer 60

A large (high or wide) therapeutic index indicates that a drug is relatively safe.

Question 61

A small (low or narrow) therapeutic index indicates

Answer 61

a small (low or narrow) therapeutic index indicates that a drug is relatively unsafe.

Question 62

In terms of therapeutic index, for a drug to be truly safe:

Answer 62

if a drug is to be truly safe, the highest dose required to produce therapeutic effects must be substantially lower than the lowest dose required to produce death.

Question 63

What does a drug with nonselective effects mean?

Answer 63

If a drug interacts with multiple receptors, its effects will be nonselective.

If a drug interacts with only one type of receptor, but that receptor type regulates multiple processes, then the effects of the drug will be nonselective.

Question 64

If a drugs is relatively selective, what does that mean?

Answer 64

If a drug interacts with only one type of receptor, and if that receptor type regulates just a few processes, then the effects of the drug will be relatively selective.