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Pharmacodynamics Flashcards

1
Q

Define Pharmacodynamics

A

The pharmacologic effect of a drug once the drug-receptor complex is formed. “What the drug does to the body”

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2
Q

Describe the Law of Mass Action?

A

The Law of Mass Action is a principle that states that the pharmacologic effect of the drug is expressed once the drug-receptor complex is formed.

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3
Q

The interaction of a ligand/drug at its binding site on the receptor complex is governed by 2 which 2 important concepts?

A

1) Affinity - A measure of the attraction between drug and its receptor site.
2) Intrinsic Activity - The effect the drug has when it interacts with a receptor site.

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4
Q

Both the Affinity and the intrinsic activity are determined by __________?

A

Chemical Structure

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5
Q

Concentration vs. Response Curves depicts the relationship between the dose of the drug and its resulting pharmacologic effect and is characterized by differences in which 4 parameters?

A

1) Potency
2) Slope
3) Efficacy
4) Individual Responses

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6
Q

Define EC50?

A

EC50 (half-minimally effective concentration) is the concentration associated with 50% of peak drug effect and is a measure of drug potency.

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7
Q

Demine Emax?

A

The maximum possible drug effect, which means that no further increases in drug dose will produce a greater effect.

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8
Q

Define Potency?

A

The quantity of a drug needed to produce a specific drug effect. The potency of a drug is depicted by its dose axis of the dose-response curve.

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9
Q

Factors affecting Potency?

A

1) Absorption
2) Distribution
3) Metabolism
4) Excretion
5) Affinity for the receptor

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10
Q

What is Effective Dose?

A

The dose required to produce a specific effect. The lower the ED, the more potent the drug. Increased affinity of a drug for its receptor moves the dose-response curve to the left (more potent).

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11
Q

Define the following terms referring to potency:

1) ED50
2) C50
3) ED90
4) LD50

A

1) ED50 (Median Effective Dose) - Dose required to produce a specific effect in 50% of people taking the drug.
2) C50 - Concentration associated with 50% of peak drug effect.
3) ED90 - Dose required to produce a specific effect in 90% of people taking the drug.
4) LD50 (Median Lethal Dose) - Dose required to produce death in 50% of people taking it.

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12
Q

Define Efficacy? Where is efficacy located on the concentration vs response curve?

A

A measure of the intrinsic ability of a drug to produce a given physiologic or clinical effect. Efficacy refers to the position of the concentration versus response curve in the y-axis and Emax is depicted by the plateau of dose-response curve.

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13
Q

The difference between a full agonist, a partial agonist,, and an antagonist represents differences in _________?

A

Efficacy

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14
Q

In terms of Potency and Efficacy, which is more clinically important?

A

Efficacy

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15
Q

Define Therapeutic Index? How is it calculated?

A

The Margin of Safety or the difference between the dose of a drug that produces a desired effect and the dose that produces undesirable effects. It is calculated by taking the ratio between the median lethal dose and the median effect dose:
(LD50/ED50)

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16
Q

Define Therapeutic Window?

A

The range of steady-state concentrations of drug that provides therapeutic efficacy with minimal toxicity.

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17
Q

Give examples of drugs with a narrow therapeutic window?

A

1) Aminoglycosides
2) Digoxin
3) Phenytoin

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18
Q

(T/F?) You can have side effects when the drug concentration is within the therapeutic window?

A

True

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19
Q

Pharmacokinetic causes for variations in drug response between individuals?

A

1) Absorption (Bioavailability)
2) Distribution
3) Metabolism
4) Excretion

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20
Q

Pharmacodynamic causes for variations in drug response between individuals?

A

1) Drug concentrations at the the site of resceptor
2) Receptors are dynamic and their function may be up- or down-regulated.
3) pH balance effects the degree of ionization

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21
Q

Examples of Genetic Disorders that can effect the individual’s drug responses.

A

1) Butyrlcholinesterase (formerly pseudocholinesterase) deficiency - PT lacks the enzyme that breaks down the neuromuscular blocking agent succinylcholine or mivacurium leading to prolonged neuromuscular blockade - PT won’t be able to breathe on their own for hours).
2) G6PD Difficiency - certain meds can cause a hemolytic anemia.
3) Intermittent Porphyria (purple urine) - Barbituates can evoke an acute attack.
4) Warfarin variability - Polymorphisms in CYP450 enzyme and receptor VKORC1

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22
Q

Reasons why PTs with advanced age have more varying drug responses?

A

1 ) TBW decreased

2) Lean body mass decreased
3) Cardiac out put and liver blood flow decreased
4) Plasma protein binding decreased
5) Decreased renal function
* All the above play a role in the chance of drug accumulation and risk of drug toxicity development.

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23
Q

Why should the CRNA be especially cautious with the PT who is known to have Myasthenia Gravis?

A

These patients have a decreased number of post-synaptic nicotinic receptors on skeletal muscles. So they have less reserve at the neuromuscular junction and are exquisitely sensitive to muscle relaxants that act on the nicotinic acetylcholine receptor.

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24
Q

What is an isomer?

A

Isomers are compounds that have the same molecular formula.

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25
Q

What is a Stereoisomer?

A

A particular kind of isomer that are different from each other ONLY in the way the atoms are oriented in space (but are like one another with respect to connectivity).

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26
Q

What are What are Enantomers?

A

Enantomers are a pair of molecules existing in two forms that are mirror images of one another but cannot be superimposed.

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27
Q

Can Enantomers interact with drug receptors the same way?

A

No - they are “stereospecific”.

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28
Q

All Enantomers contain a Chiral carbon. What is a Chiral Carbon?

A

Chiral is a term used to describe a molecule that has a non-superimposable mirror image. It also describes a molecule that has a center (or centers) of 3-dimensional asymmetry.

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29
Q

How can you distinguish between Enantomers that are dissolved in a solution?

A

By the direction that rotates polarized light:

1) (d or +) - rotates polarized light the right/clockwise
2) (l or -) - rotates polarized light to the left/counterclockwise.

30
Q

What is a racemic mixture? How does a racemic mixture rotate polarized light?

A

A racemic mixture is a solution in which two enantiomers are present in equal proportions. A racemic mixture does not rotate polarized light.

31
Q

How are Enantomers named?

A

Enantomers are named by the configuration of molecules:

1) S (sinnister); R (rectus) designation
2) D and L designation

32
Q

(T/F?) The binding of a chemical to receptor is Stereospecific?

A

True - Both the affinity of a drug for its receptor and its intrinsic activity are intimately related to the drugs chemical structure.

33
Q

What are some examples of Racemic Mixtures used in anesthesia?

A

1) Thiopental and Methohexital
2) All volatile anesthetics except sevoflurane
3) Ketamine
4) Local anesthetics such as bupivicaine and Prilocaine
5) Albuterol
6) Ephedrine

34
Q

Characteristics of the two Ketamine Enantomers?

A

1) S(+) form - has greater NMDA receptor affinity, is more potent and it less likely to produce emergence delirium.
2) R(-) form - is weaker and produces emergence delirium.

35
Q

Bupivicaine is administered as a racemic mixture. What are the characteristics of the two enantiomers?

A

1) S-isomer (Levobupivicaine) - associated with less cardiac toxicity.
2) R-isomer - more cardiac toxicity and is thought to predominately cause the cardiac toxicity from bupivicaine.

36
Q

Define the following terms as it relates to Pharmacodynamics:

1) Hyperactive
2) Hypersensitive
3) Hypoactive

A

1) Hyperactive - low doses of medication leads to a higher than expected effect
2) Hypersensitive - When a patient is allergic (sensitive) to a drug.
3) Hypoactive - high doses of a medication required to evoke desired effect (resistant to drug).

37
Q

Define the following terms as it relates to Pharmacodynamics:

1) Tolerance
2) Cross-tolerance
3) Tachyphylaxis

A

1) Tolerance - Hyporeactivity that is queried from chronic exposure to a drug.
2) Cross-tolerance - Tolerance to a drug that develops through continued use of another drug with similar pharmacologic effects (i.e. volatile anesthetics and alcohol use)
3) Tachyphylaxis - Tolerance that develops rapidly only after a few doses (i.e. loss of drug response after a few doses).

38
Q

What are the 4 mechanisms of drug tolerance?

A

1) Cellular tolerance - the most important factor in the development of tolerance drugs such as opioids, barbiturates, and alcohol is neuronal adaptation.
2) Decrease in the number of receptors
3) Enzyme induction
4) Decreased neurotransmitter release

39
Q

Define the following terms as it relates to Pharmacodynamics:

1) Immunity

2) Idiosyncrasy

A

1) Immunity - Hyporeactivity to a drugs effect due to presence of antibodies
2) Idiosyncrasy - Describes the unusual effect occurring in individual, regardless of intensity or dosage. (i.e. diphenhydramine in some PTs can cause stimulation/excitation).

40
Q

Define the following terms as it relates to Pharmacodynamics:

1) Additive Effect
2) Synergistic Effect
3) Antagonistic Effect

A

1) Additive Effect - The 2nd drug adds to the effect of the first (i.e. two inhaled anesthetics)
2) Synergistic Effect - The two drugs interact to produce and effect greater than the sum of the two individual drugs (i.e. mepivivcaine and bupivicaine
3) Antagonistic Effect - Two drugs interact to cause a lesser effect than each individual drug would’ve (i.e. fentanyl (opioid antagonist) and naloxone (opioid antagonist).

41
Q

What is an Agonist?

A

An activator which mimics the expected receptor response?

42
Q

What is a Full Agonist?

A

An agonist that has a high efficacy or high intrinsic activity, n that each drug-receptor interaction causes a strong enough stimulus to tissue that a full/maximal response is possible.

43
Q

What is a Partial Agonist?

A

Aa drug that has affinity for a receptor but has low efficacy or intrinsic activity at the receptor compared to a full agonist, so that even when all the receptors are occupied, the stimulus to the tissue is insufficient to generate a maximal response.

44
Q

What happens when a partial agonist is given with a full agonist?

A

They compete for receptor sites and the response will less than if the full agonist was given alone. (i.e. Buprenophine (partial agonist at the opioid receptor) and morphine (full agonist at the opioid receptor).

45
Q

What is an Antagonist?

A

A drug that binds to a receptor without activating the receptor (has affinity for a receptor but lacks intrinsic activity).

46
Q

4 examples of Antagonists?

A

1) Naloxone - narcotic antagonist
2) Atropine - Blocks the effects of Each at the muscarinic receptor
3) Metoprolol, Propranolol & Esmolol - Blocks the effects at beta-adrenergic receptors.
4) Flumazenil - Blocks the effects of diazepam at the benzodiazepine receptor.

47
Q

What is a competitive Antagonist?

A

An antagonist that binds to a receptor at the same site and the endogenous ligand or agonist, but without activating the receptor. `

48
Q

The log dose-effect curve for the agonist is shifted to the _______ by a competitive antagonist.

A

Right

49
Q

What is a competitive reversible antagonist?

A

Same thing as a competitive Antagonist - An antagonist that binds reversibly to the receptor and for the antagonist to work it must be greater in number than the agonist.

50
Q

(T/F?) All non-depolarizing neuromuscular blocking agents are examples of competitive reversible antagonists.

A

True

51
Q

Non-competitive Irreversible Antagonist vs. Non-competitive pseudo-Irreversible Antagonist ?

A

1) Non-competitive Irreversible Antagonist binds permanently via covalent bonds.
2) Non-competitive pseudo-Irreversible Antagonist - binds so tightly that it dissociates very slowly from receptor.

52
Q

(T/F?) You CAN NOT overcome non-competitive antagonist regardless of how much agonist you add and the maximal effect CAN NOT be reached?

A

True

53
Q

In Non-competitive Irreversible Antagonist, the old dose-effect curve is shifted ________?

A

downward and slightly to the right

54
Q

What is an Allosteric Non-competitive Antagonist?

A

An antagonist that binds to a separate binding site from the agonists binding site on the same receptor and does not compete.

55
Q

An Allosteric Non-competitive Antagonist shifts the log dose-effect curve _______?

A

Downward

56
Q

What is Allosteric Potentiation? Give an example?

A

A form of agonist in which a compound acts at an allosteric site and ENHANCES the affinity of the normal agonist at its binding site. i.e. Benzes and some anesthetics act at allosteric sites on the GABAa complex to increase the affinity of GABA for its binding site.

57
Q

2 major functions of receptors?

A

Ligand binding and signal transduction/message propagation

58
Q

2 functional domains of of receptors?

A

1) Ligand-binding domain

2) Effector domain

59
Q

Up-regulation vs. Down-regulation

A

1) Up-regulation - Increase in the number of receptors because of a lack of use.
2) Down-regulation - Decrease in the number of receptor because of overuse.

60
Q

How can diseases alter receptor function?

A

1) By mimicking a ligand receptor over-activity
2) By mimicking a ligand and causing inhibition or down-regulation .
3) By attacking and destroying receptors

61
Q

Types of bonds that occur between drugs and receptors?

A

1) Covalent - strongest (irreversible)
2) Ionic - acidic and basic drugs
3) Hydrogen
4) Van Der Waal Forces - weak bonds

62
Q

How are the CNS effects that happen after a bolus injection of IV anesthetics primarily terminated?

A

By Distribution

63
Q

(T/F?) The larger the therapeutic index of a drug, the safer the drug is for administration

A

True

64
Q

3 things that can alter both Pharmacodynamics and Pharcokinetic aspects of drug response in individuals?

A

1) Genetic variations
2) Patient physiology
3) Drug Interactions

65
Q

(T/F?) An enantiomer can have more than one chiral carbon?

A

True - Labetolol has 4 chiral carbons

66
Q

What is an Inverse Agonist?

A

a drug that binds selectively to the inactive state of the receptor and shifts the conformational equilibrium of the receptor to the inactive state. opposite effect of a receptor agonist. i.e. antihistamine drugs at histamine-1 , propranolol and metoprolol.

67
Q

2 locations of receptors?

A

1) Cell membrane

2) Inside the cell (cytosol or nucleus)

68
Q

Ways of terminating a drug’s response?

A

1) Metabolism via liver or Hoffman degradation
2) Excretion - via kidney or biliary system
3) Redistribution

69
Q

On the dose response curve, what are the following values representing:

1) X-axis
2) Y-axis
3) Slope

A

1) X-axis - Potency
2) Y-axis - Efficacy
3) Slope - How many receptors must be occupied to illicit a response

70
Q

Are the following drugs full, partial, antagonists or reverse agonists:

1) Propanolol
2) Cisatricurium
3) Propofol
4) Nalbuphine

A

1) Propofol - Full agonist
2) Nalbuphine - Partial agonist
3) Cisatricurium - Antagonist
4) Propanolol - Inverse Agonist

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