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Systemic Pharmacology I > Pharmacodynamics > Flashcards

Pharmacodynamics Flashcards

1
Q

pharmacodynamics

A

the actions of a drug on a living organism

  • mechanism of action
  • receptor interaction
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2
Q

a drug can modify a particular ____

A

cellular function or the rate of that function

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3
Q

a drug can’t impart ____ to a cell or target tissue

A

a new function

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4
Q

drug effect depends on ____

A

what the cell is capable of accomplishing

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5
Q

drugs must ____ to have an effect

A

interact with a molecular target

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6
Q

target is usually referred to as a ____

A

receptor

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7
Q

selectivity of drug action is due to ____

A

receptors

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8
Q

action of agonists and antagonists is mediated by ___

A

receptors

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9
Q

when a drug binds to a receptor, one of the following usually occur:

A
  • an ion channel is opened or closed
  • biochemical messengers (second messengers) are activated (initiate a series of chemical reactions)
  • a normal cellular function is inhibited
  • a cellular function is “turned on” (ex: DNA transcription)
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10
Q

Law of Mass Action:

-the combinations of drug (ligand) and receptor depends on ____

A

the concentrations of each

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11
Q

Law of Mass Action:

-the amount of drug-receptor complex formed determines the ____

A

magnitude of the response

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12
Q

Law of Mass Action:

-a minimum number of drug-receptor complexes must be formed for ____

A

a response to be initiated (threshold)

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13
Q

Law of Mass Action:

-as drug concentration increases, the number of drug-receptor complexes ____ and drug effect ____

A

increases;

increases

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14
Q

Law of Mass Action:

  • a point will be reached at which all receptors are bound to a drug
  • no further ____ can be formed
  • response ____
A

complexes;

does not increase any further (saturation)

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15
Q

drug-receptor complex formation is proportional to the concentrations of drug and receptor, but the relationship is not ____; pharmacologists usually use a ___ graph to ____

A

linear;
semilogarithmic;
linearize the relationship

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16
Q

drug response is regulated by 2 properties:

A

1) affinity- the ability of the drug to bind to its receptor

2) efficacy- the ability of the drug to alter the activity of its receptor

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17
Q

affinity

A

the strength with which a drug forms a complex with its receptor

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18
Q

affinity is influenced by:

A
  • size and shape of drug molecules
  • types, number, and spatial arrangement of drug binding sites (stereochemistry)
  • intermolecular forces between drug and binding sites
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19
Q

drug concentration effect on affinity

A

NONE

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20
Q

types of intermolecular forces

A
  • Van der Walls forces
  • hydrogen bonds
  • covalent bonds
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21
Q

Van der Walls forces

A
  • weak bonds
  • transient
  • reversible
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22
Q

hydrogen bonds

A
  • intermediate bonds
  • transient
  • reversible
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23
Q

covalent bonds

A
  • strong bonds

- long-lasting and/or irreversible

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24
Q

binding of drug to receptor usually involves ___ bonds

A

weaker

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25
Q

there is a continuous ____ of the drug with the receptor as long as the drug is present

A

association and dissociation

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26
Q

the ___ is a measure of a drug’s affinity

A

dissociation constant (Kd)

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27
Q

Kd represents the ____

A

concentration of drug needed to ensure that 50% of the total receptor population is bound to the drug

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28
Q

Kd does not always indicate ____

A

half-maximal response

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29
Q

each drug-receptor combination will have a characteristic Kd value;
high affinity= _____ value for Kd
low affinity= _____ value for Kd

A

small;

large

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30
Q

a cell will respond only to the spectrum of drugs that exhibit ____

A

affinity for the receptors expressed by the cell

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31
Q

the greater the affinity for one receptor, the ____, which ____

A

more selective the drug’s actions;

lowers the potential for side effects

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32
Q

few drugs are entirely ____ for one receptor;

many are ____ towards certain receptors based on affinity

A

specific;

selective

33
Q

as concentration increases, the drug will bind to receptors for which it has ____

A

lower affinity

34
Q

only those tissues ____ will respond to the drug

A

possessing receptors

35
Q

the more restricted the distribution of drug receptor, the _____

A

more selective will be the effects of drugs that interact with that receptor

36
Q

dose-response curve

A

gives representation of the relationship between amount of drug given and the anticipated effect

37
Q

2 types of dose-response curves

A
  • graded

- quantal

38
Q

graded dose-response curve:

  • measures ____
  • similar shape to ____
  • key points: ____
A

continual effect;
drug-receptor occupancy curve;
Emax, EC50

39
Q

Emax (graded dose-response curve)

A

dose beyond which no further response is achieved (maximal effect); measure of efficacy

40
Q

EC50

A

concentration (dose) that produces 50% of maximal response; measure of potency

41
Q

quantal dose-response curve:

  • measures ____
  • gives the relationship between ____
  • key points: ____
A

responses that are all or none;
drug dose and the frequency with which a biologic effect occurs;
ED50, Emax

42
Q

ED50

A

dose of drug that produces a response in 50% of the population

43
Q

Emax (quantal dose-response curve)

A

dose at which all of the patients respond to the drug

44
Q

quantal dose-response curve:

-can be plotted for _____ effects

A

therapeutic, toxic, and lethal

45
Q

TD50

A

dose that produces toxic effects in 50% of the patient population

46
Q

LD50

A

dose at which 50% of patients die

47
Q

therapeutic index (TI)

A

a measure of the safety of a drug (larger is better!);

found by dividing the LD50 (or TD50) by the ED50

48
Q

agonist

A

binds to receptor and elicits a response

49
Q

antagonist

A

binds to receptor but does not elicit a response

50
Q

full agonists

A

produce maximum activation of the receptor and elicit a maximum response from the tissue

51
Q

partial agonists

A

produce weaker activation than full agonist or endogenous ligand; must be bound to more receptors to produce same effect as full agonist

52
Q

inverse agonists

A

inhibit receptors that exhibit activity in the absence of agonist binding; binding of inverse agonist reduces the baseline activity of the receptor; technically an agonist because it causes a response

53
Q

antagonists

A

have zero intrinsic activity; do not cause a reaction, simply prevent the receptor from being occupied by another molecule

54
Q

competitive reversible antagonists

A
  • antagonist competes directly with the agonist molecule
  • increasing the concentration of the agonist will eventually overcome the antagonism
  • Emax is the same but curve shifted to the right
55
Q

competitive irreversible antagonists

A
  • compete directly with agonist for receptor binding site
  • bond is so strong that it is irreversible
  • permanently reduces number of receptors available to an agonist
  • reduces the maximal agonist effect
56
Q

noncompetitive antagonist

A
  • do not compete with agonist for same binding site
  • impair the ability of the agonist to bind to or activate the receptor
  • both antagonist and agonist can be bound at the same time
  • increasing concentration of agonist will not reverse the inhibitory action
  • similar curve to irreversible agonist
  • difference may be in duration of action
57
Q

4 families of receptors

A
  • ligand-gated ion channels
  • G protein-coupled receptors
  • enzyme-linked receptors
  • intracellular receptors
58
Q

ligand-gated ion channels

A
  • regulates ion flow across membranes
  • flow of ions through these channels is dependent on binding of a ligand (neurotransmitter, drug) to the receptor on the channel
  • ion channel possesses a receptor for an endogenous ligand (agonist usually binds to same receptor)
  • activation by endogenous ligand or agonist opens the channel (antagonists prevent activation of the channel or cause it to remain closed)
59
Q

ligand-gated ion channel examples

A
  • cholinergic receptors: found in nervous system, binding of agonist opens sodium channels and causes initiation of action potential
  • GABA receptors: found in CNS, binding of agonist opens chloride channels, causing hyperpolarization (reduce probability of action potential)
60
Q

voltage-gated ion channels

A
  • change conformation in response to changes in membrane voltage
  • binding of drugs to these channels causes a change in the response of the channel
  • open, closed, or inactive state may be lengthened or shortened
  • ex: local anesthetics
61
Q

G-protein coupled receptors

A
  • single peptide that has seven membrane-spanning regions
  • linked to a G-protein
  • binding of ligand to the extracellular region of the receptor activates the G-protein
62
Q

G-protein has ___ subunits: ____

A

3;

alpha, beta, and gamma

63
Q

activation of G-protein coupled receptors

A
  • GTP replaces GDP on the alpha subunit
  • alpha-GTP and beta-gamma subunits dissociate and interact with other cellular effectors (enzymes or ion channels)
  • change the concentrations of intracellular second messengers that are responsible for further actions within the cell
  • slightly slower response but lasts longer (several seconds to minutes, “slow on” and “slow off”)
64
Q

second messengers are important in ____

A

conducting and amplifying signals from G-protein coupled receptors

65
Q

enzyme-linked receptors

A
  • have cytosolic enzyme activity as part of their structure and function
  • binding of the ligand to the receptor activates or inhibits the activity of the enzyme
  • receptor undergoes conformational change upon binding
  • longer duration (minutes to hours)
66
Q

enzyme-linked receptors:

  • ____ can modify the three-dimensional structure of the target protein
  • acts as a ____
  • ____ that multiplies initial signal
  • examples: ___
A

addition of a phosphate group;
molecular switch;
cascade activation;
insulin receptor, VEGF

67
Q

intracellular receptors

A
  • receptors are located intracellularly
  • ligand must be lipid soluble
  • example: steroid hormones
  • binding of ligand with its receptor causes dissociation of a small repressor peptide and activates the receptor
  • complex migrates to the nucleus where it binds to specific DNA sequences
  • results in regulation of gene expression
  • much longer time course (due to change in gene expression, 30 mins or more to observe response, response lasts hours to days)
68
Q

spare receptors

A
  • in some cases, a maximal response can be achieved when only a fraction of receptors are occupied (EC50 is much lower than the Kd)
  • due to amplification of signal duration and intensity
  • common with G-protein linked receptors
69
Q

spare receptors:

amplification occurs by two phenomena

A
  • a single ligand receptor complex can interact with many G-proteins
  • an activated G-protein can persist for a longer duration than the original ligand-receptor complex

-because the amplification only involves a fraction of the total receptors for a specific ligand, the system is said to have spare receptors

70
Q

receptor desensitization

A
  • repeated or continuous administration of a ligand may lead to changes in the responsiveness of the receptor
  • evolved to prevent cell damage
71
Q

two mechanisms of receptor desensitization

A
  • tachyphylaxis

- endocytosis

72
Q

receptor desensitization: tachyphylaxis

A

receptor is still present but is unresponsive to the ligand

73
Q

receptor desensitization: endocytosis

A
  • binding causes conformational change in receptor

- receptor undergoes endocytosis and is sequestered from further activation

74
Q

tolerance

A
  • decreased response to a drug
  • dose must be increased to achieve the same effect
  • can be metabolic, cellular (downregulation), or behavioral
75
Q

dependence

A
  • patient needs a drug to function “normally”

- usually physical but CAN have a psychological component

76
Q

withdrawal

A
  • drug is no longer given to a dependent patient

- symptoms are often the opposite of the effect of the drug

77
Q

there may be considerable variation in the way that patients respond to medication for multiple reasons:

A
  • alteration in the concentration of drug that reaches the receptor
  • variation in concentration of endogenous ligand
  • alteration in number of receptors
  • changes in components of response
78
Q

most drugs interact with receptors that will determine ____

A

selective therapeutic and toxic effects of the drug

79
Q

receptors largely determine the _____

A

quantitative relations between dose of a drug and pharmacologic effect

Systemic Pharmacology I (7 decks)

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