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Pharmacology Test 1 > Uptake & Distribution > Flashcards

Uptake & Distribution Flashcards

1
Q

Define Pharmacodynamics

A

What drug does to the body

  1. Mechanism of effect
  2. Sensitivity
  3. Responsiveness
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2
Q

Define Pharmacokinetics

A

What your body does to the drug

  1. Absorption
  2. Distribution
  3. Metabolism -liver
  4. Excretion - kidneys
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3
Q

Commonly measured parameters of injected drugs are?

A
  1. Elimination half-life
  2. Bioavailability
  3. Clearance
  4. Volume of distribution Vd
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4
Q

Define the Compartmental Model

A

Divides body into two compartments that represent THEORETICAL spaces with CALCULATED volumes.

  1. Central
  2. Peripheral (reservoir)
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5
Q

Which compartment has a RAPID uptake of a drug?

A

Central

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6
Q

Which compartment is made up of highly perfused tissues and intravascular fluid?

A

Central

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7
Q

Which compartment is the drug FIRST introduced into

A

Central

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8
Q

Which organs make up the central compartment?

A

Kidney, lungs, liver, heart, brain

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9
Q

How much CO does the central compartment receive?

A

75%

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10
Q

How much CO does the peripheral compartment receive?

A

25%

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11
Q

How much body mass does the Central compartment contain?

A

10%

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12
Q

How much body mass does the reservoir contain?

A

90%

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13
Q

What causes a decrease in the rate of transfer between the Central compartment and the Peripheral compartment?

A

Aging

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14
Q

Why do you decrease dosage of drugs (eg Thiopental) in the elderly?

A

There is a lag due to the slowed rate of transfer between compartments leading to a greater plasma concentration in certain drugs.

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15
Q

What happens when the plasma drug concentration declines below tissue drug concentration?

A

the drug leaves the tissues and re-enters the circulation

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16
Q

Why do you shut off anesthetic gases/TIVA early in the obese population?

A

Fat acts as a reservoir that maintains plasma concentration and prolongs the effect of a drug.

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17
Q

What effect can large or repeated doses of a drug have on redistribution?

A

Negate redistribution, prolonging duration of action by saturating inactive tissue to a point where effect depends on metabolism of the drug rather than redistribution.

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18
Q

What body tissues make up the peripheral compartment?

A

Muscle groups, Fat group, Vessel-poor group

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19
Q

Lungs act as a reservoir for what kind of drugs?

A

Lipophilic drugs (lidocaine, fentanyl, Demerol)

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20
Q

What drugs do not cross the blood-brain barrier into the brain circulation?

A

Ionized, water soluble drugs.

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21
Q

What drugs CAN cross the Blood-brain barrier?

A

Lipophilic drugs

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22
Q

How do you overcome the blood brain barrier? (4 ways)

A
  1. Large doses of drug
  2. Head injury
  3. Hypoxemia
  4. Old age
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23
Q

What is the Biophase?

A

Also called the “effect site”, where drugs exert their biological effect. The immediate milieu where drugs act upon the body including:

  1. Membranes
  2. Receptors
  3. Enzymes
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24
Q

What is the biophase of muscle relaxants?

A

Muscles

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25
Q

What is the biophase of anesthetics?

A

The brain (effect site)

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26
Q

What is the rate constant of drug elimination from the effect site/biophase ? (I.e. rate eliminated from the brain if the drug is an anesthetic)

A

Ke0

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27
Q

Formula for Vd?

A

Vd = (Dose of IV drug) / (plasma concentration before elimination)

Eg: dose 50mg, plasma conc prior to elimination 10mg/L
(50mg) / (10mg/L) = 5L Vd

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28
Q

What is Volume of distribution Vd?

A

Sum of all the volumes of the theoretical compartments that constitute the Compartmental Model. How quickly does the dose occupy space.

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29
Q

Vd is influenced by? (3 things)

A
  1. Lipid solubility (matters most)
  2. Binding to plasma proteins
  3. Molecular size
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30
Q

What is lipid solubility? How does it contribute to Vd?

A

More lipophilic = more Vd (quicker it can distribute to all spaces in the body). Matters more than protein binding.
Eg: drug is highly protein bound but super lipophilic, available drug will have a large effect.

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31
Q

How does binding to plasma protein effect Vd?

A

Highly bound drugs cant cross membranes (BBB) = lower Vd. Drugs that are bound to plasma proteins will UNBIND as elimination begins.

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32
Q

How does molecular size affect Vd?

A

Smaller size = higher Vd (can cross the BBB readily)

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33
Q

Time necessary for plasma[] of drug to decline 50% during the elimination p0hase

A

Elimination half time

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34
Q

Elimination half time is ______ (direct/indirect) proportional to its Vd

A

Directly

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35
Q

Elimination half time is _______ (independent/dependent) on the dose of drug administered

A

Independent

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36
Q

Time necessary to eliminate 50% of the drug from the body

A

Elimination half-life

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37
Q

What happens if dosing intervals are less than the elimination half times?

A

Drug accumulation

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38
Q

What happens when the plasma [ ] decrease doesn’t parallel its elimination from the body?

A

Elimination half time and elimination half life are NOT equal

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39
Q

Elimination half life is always greater than elimination half time (True/false)

A

True; plasma [ ] will always be less than the total body [ ]

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40
Q

If a drug undergoes 3 half-times, what percent of initial amount is eliminated?

A

87.5

3 half-times; 1/8 is the fraction of initial amount remaining… so 7/8 has been eliminated… 7/8 = 87.5

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41
Q

Why is the distribution phase part of the Plasma Concentration Curve so rapid?

A

Rapid drop as the drug goes from the central —> peripheral compartment

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42
Q

What does the Beta distribution part of the Plasma Concentration Curve represent

A

Elimination phase

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43
Q

Context sensitive half-time refers to ____

A

Discontinuing an IV infusion.

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44
Q

Define context-sensitive half-time

A

Time required for plasma [ ] of a drug to decrease by 50% after discontinuation of drug administration.

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45
Q

What does the context sensitive half time depend on?

A

1) Distribution
2) Excretion
3) Physiochemical properties (lipid solubility, size, protein binding) of the drug
4) length of infusion

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46
Q

Systemic absorption (regardless of route) depends on ___

A

The drug’s SOLUBILITY

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47
Q

The most convenient & most economic route is ______

A

PO

48
Q

Disadvantages of the PO route in terms of drug absorption

A
  1. Emesis
  2. Destruction by enzymes (1st pass effect) or acidic gastric fluid
  3. Irregular absorption w. Food or other drugs.
49
Q

Define the First pass effect

A

Drugs absorbed via the GI system enter the portal venous blood flow and pass through the liver before entering the systemic circulation. Here they are extensively extracted and metabolized

50
Q

How do drugs absorbed in the GI system get to the liver?

A

Via the portal venous blood supply

51
Q

Which routes bypas the liver and prevents the first pass effect?

A

Sublingual, transmucosal, IV, Rectal (distal rectum), transdermal

Anything that avoids the GI system

52
Q

Punctured nifedipine capsules & CBD oil are examples of what kind of route? What is the benefit?

A

Sublingual; prevent the first pass effect

53
Q

Which route provides a sustained therapeutic plasma [ ] of a drug?

A

Transdermal

54
Q

How does transdermal absorption work?

A

Drug enters via sweat ducts & hair follicles which function as diffusion shunts.

55
Q

What is the rate-limiting step in transdermal absorption?

A

Diffusion across the stratum corners of the epidermis. Thickness and blood flow are factors reflected in the skin’s permeability for drugs.

56
Q

Proximal vs Distal rectum

A

Proximal —> GI, portal system, liver = First pass effect

DIstal —> bypasses portal system

57
Q

Why is the rectal route unpredictable?

A

Distal vs proximal administration … if the drug is too far in (proximal) then it is susceptible to the first pass effect.

58
Q

Which route will achieve therapeutic plasma levels precisely & rapidly

A

IV

59
Q

Which form (ionized/non-ionized) of a drug can diffuse across lipid cell membranes (BBB, renal, tubules, GI epithelium, hepatocytes)?

A

Non-ionized, lipid soluble

60
Q

Which fraction of a drug is pharmacologically ACTIVE

A

Non-ionized form

61
Q

Which form a drug will undergo re-absorption across renal tubules, absorbed from the GI tract and metabolized by liver?

A

Non-ionized

62
Q

Which form of a drug is excreted by the kidneys unchanged?

A

Ionized

63
Q

Why cant ionized drugs cross the lipid cell membrane?

A

Repelled from portion of the cell with similar charges.

64
Q

Weak acid drug is administered to an acidic patient… should you increase or decrease the dose? Why?

A

Decrease dose since less ionization is happening.

65
Q

A weak base drug is administered to an acidic patient. Should you increase or decrease the dose? Why?

A

Increase dose due to increased ionization of drug.

66
Q

What does the degree of ionization depend on?

A

Dissociation constant pK of drug & pH of surrounding environment

67
Q

How does ion trapping happen?

A

A membrane separates two different pH environments, once a drug crosses the membrane (i.e. placenta) into a more acidic/basic environment and ionizes in the new environment it wont cross back over the membrane and end up building up (in the fetus) in its ionized form (can eventually be excreted by kidneys of baby, however since the BBB may not be fully developed, the ionized form may cross the BBB when its not supposed to)

68
Q

What protein binds to acids?

A

Albumin

69
Q

What protein binds to bases

A

Alpha acid glycoproteins

70
Q

Which form of a drug will readily cross the cell membrane? (Protein bound/unbound)

A

Unbound

71
Q

What happens to protein binding when plasma [ ] of drug decreases?

A

The drug will unbind from the protein and become available

72
Q

True/False More protein binding = longer effect

A

True (generally) - because if drug is protein bound, it cant cross into the liver for elimination so it stays around longer until it is unbound.

73
Q

When can a protein-bound drug be metabolized/excreted?

A

Once it unbinds

74
Q

Vd is ___ (direct/inversely) proportional to protein binding

A

Inversely

75
Q

Which drugs will be markedly effected by alterations in protein binding?

A

Highly protein bound drugs: Warfarin, propranolol, phenytoin, diazepam

76
Q

Define clearance

A

Volume of plasma cleared of drug by metabolism and excretion

77
Q

When drug administered (in therapeutic dose ranges) is cleared at a rate PROPORTIONAL to the amt drug present in plasma… this is

  1. First order kinetics
  2. Zero order kinetics
A

First order kinetics

78
Q

When drug administered exceeds metabolic or excretory capacity of the body to clear drugs and a CONSTANT AMOUNT of drug is cleared per unit of time (eg 2mg/hr) this is

  1. First order kinetics
  2. Zero order kinetics
A

Zero order kinetics

79
Q

Drugs who clear via Zero Order Kinetics principle

A

ASA, DIlantin, ETOH

80
Q

When hepatic extraction is higher than 0.7, the clearance of the drug will depend on_____

A

Hepatic blood flow

“Perfusion-dependent elimination”

81
Q

If hepatic extraction ratio is less than 0.3, ____ and ____ will aid in hepatic clearance

A

Decrease in protein binding & Increase in enzymatic activity
“Capacity - dependent elimination”

Changes in hepatic blood flow will have minimal changes in its clearance.

82
Q

Most important organ for elimination of unchanged drugs or their metabolites

A

Kidney

83
Q

Water soluble compounds are excreted ____ (more/less) efficiently by kidneys than lipid soluble drugs

A

More

84
Q

Usually a drug has to be _____ or ______ to be excreted via urine

A

Ionized or SMALL lipophilic

Lg lipophilic drugs will be reabsorbed… unchanged drug is not excreted in urine.

85
Q

How do you turn a lipophilic drug into a form where it can be excreted?

A

Metabolize it! Bio transformation from pharmacologically active into water soluble/inactive/ionized form.

86
Q

What does it mean if a drug is X amount “excreted unchanged”

A

Portion will never have an effect (ionized) and will go straight to the kidneys for excretion (be aware of pats with Kidney failure!)

87
Q

Increased water solubility ___ (inc/dec) the Vd of a drug and enhances renal excretion

A

Decreases

88
Q

Why is metabolism not equal inactivation/detox of a drug?

A

Some metabolites are active

89
Q

4 pathways of metabolism

A
  1. Oxidation
  2. Reduction
  3. Hydrolysis
  4. Conjugation
90
Q

What happens in Phase 1 of metabolism

A

oxidation, reduction, hydrolysis

91
Q

What happens in Phase II of metabolism

A

Conjugation

Drug interacts with endogenous substrate to form water soluble CONJUGATES —> excreted by kidney

92
Q

Sites of metabolism

A
  1. Plasma
  2. Kidneys
  3. Lungs
  4. GI tract
  5. Liver
93
Q

What enzyme is responsible for metabolism of most drugs in the liver? Where is it located?

A

Hepatic microsomal enzymes
Located in the hepatic smooth ER

Eg: Cytochrome P-450

94
Q

6 isozymes of cytochrome P-450 involved in drug metabolism?

A

CYP1A2, CYP2D6, CYP2C19, CYP2E1, CYP2C9, CYP3A

CYP: 1a2, 2d6, 2c19, 2e1, 2c9, 3a

95
Q

What may be a reason a patient has “treatment resistant depression”? Or when cancer therapy is not working for a patient.

A

Patient does not have the proper hepatic microsomes isozyme (1 of the 6 CYP450) of the metabolic pathway to interact with drug (body wont react with it even if we are technically talking about metabolism)

96
Q

How does ETOH effect the dosage other drugs in a patient who is a frequent drinker?

A

Must INC dose b/c ETOH is an Enzyme Inducer

Repeated exposure to ETOH will stimulate the activity of enzymes…so other drugs that follow the same pathway as ETOH will be exposed to more enzymes that break it down hence larger dosages required. Larger doses of drugs and larger doses of ETOH required for desired effect.

97
Q

Which enzymes are involved in Oxidation, Reduction + Conjugation of drugs

A

Hepatic microsomal enzymes

98
Q

Which enzymes are involved in Hydrolysis (of ester bond) of drugs?

(Also does conjugation, oxidation and reduction)

A

Non-microsomal enzymes

versus hepatic microsomal enzymes that do oxidation, reduction and conjugation only

99
Q

Which enzyme is present in Liver (mostly), plasma & GI tract?

A

Non-microsomal enzyme

100
Q

Which enzymes do NOT undergo enzyme induction?

A

Non-microsomal enzymes

Vs hepatic microsomal enzymes that DO

101
Q

What is it called when you increase the concentration of receptors? Decrease?

A 
Increase = up-regulate
Decrease = down-regulate
102
Q

Why is it wrong to simply take someone off beta blockers after a while?

A

They have up-regulated their concentration of beta receptors in response to beta blockers… can cause a hypertensive crisis.

103
Q

Taking growth hormone leads to small testes due to __

A

Down-regulation.

Exogenous form of growth hormone causes the body to down-regulate the receptors.

104
Q

State of Receptor Activation Theory states:

A

Non-activated receptors can be activated by the drug.

105
Q

Receptor occupancy theory states:

A

The more receptors occupied by the drug the greater the effect.

106
Q

Non-receptor drug action

A

When there is no receptor-drug interaction eg: chelating drugs form bonds with metallic cations. Antacids neutralize gastric acid by a direct action.

107
Q

Agonist drug vs antagonist drug

A

Agonists mimic molecule and activate the SAME receptor sites causing SIMILAR effect. Eg: opioid/mu receptor
Antagonists bind to SAME receptor and change configuration of site therefore PREVENTING effect from cell signaling molecules. Eg: betablocker

108
Q

How does chemical structure affect drugs?

A

Minor modifications in structure (stereochemistry) may result in drastic change in pharmacological properties. Interaction/ with biological receptors can differ greatly even to a point of no binding. Potency can be very different (ephedrine). Side effects can be different.

109
Q

Efficacy vs Potency

A

Efficacy - ability of drug to produce desired effect

Potency - relationship between effect and dose necessary to achieve effect

110
Q

what is the median EFFECTIVE dose?

A

ED 50

Dose at which 50% of people will get the effect

111
Q

What is the median LETHAL dose?

A

LD 50

dose at which 50% will die

112
Q

How do you estimate the clinical therapeutic index?

A

Ratio of LD50 to ED50 will suggest how selective that drug is in producing its desired effect

113
Q

Define a Hyper-reactive patient

A

People in whom a LOW dose of drug produces its expected pharmacologic effect
Eg: low dose in Asian population

114
Q

Hypersensitivity

A

Allergic

115
Q

Additive effect

A

When 1+1=2

The second drug acting with first produces equal summative effect.

116
Q

Synergistic effect

A

1+1=3

Two drugs produce an effect greater than their sum

Pharmacology Test 1 (3 decks)

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