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2. Foundations of Medicine PoD > Drug Therapy > Flashcards

Drug Therapy Flashcards

1
Q

pharmacokinetics

A

the movement of drugs through the body

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2
Q

pharmacodynamics

A

the body’s biological response to drugs

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3
Q

safe and effective medications

A

balance between safety and efficacy - fine line with toxicity

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4
Q

bioavailability

A

the extent and rate at which the drug enters systemic circulation, thereby accessing the site of action

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5
Q

what does the effect of a drug depend on

A
  • affinity
  • intrinsic efficacy
  • pharmalogical effect also dependent on residence time
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6
Q

what can different drugs still do

A

ellicit the same response - due to different mechanisms/pathways

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7
Q

What are different receptors which have the same function in different people called

A

polymorphic variation - diff sequence of genes code for same receptor

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8
Q

what mechanism of binding occurs in endogenous receptors

A

lock and key - either on same site, or allosteric site

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9
Q

agonist drug

A

inc proportion of activated receptors

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10
Q

antagonist drugs

A

dec proportion of activated recptors - prevent activation

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11
Q

what 2 mechanisms can inhibition occur by

A

competetive or non-competetive

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12
Q

what is a drug steady state

A

when the quantity of drug eliminated equals the quantity of the drug that reaches the systemic circulation - kinda like equilibrium

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13
Q

what are allosteric modulators

A

drug binds to different site, changing the shape of the receptor site for the endogenous ligand - can inc or dec efficacy

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14
Q

Biophase

A

the effect site of the drug (physical region in which the drug target is located

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15
Q

what is the bioavailability if we inject a drug directly into the circulation (e.g. IV route)

A

100%

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16
Q

what is a downside of non IV routes

A

some drug is lost (e.g. gut tissues etc. and passed on for excretion)

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17
Q

what is first pass metabolism

A

drug gets metabolized at a specific location in the body that results in a reduced concentration of the active drug upon reaching its site of action or the systemic circulation - amount of drug removed before it reaches systemic circulation

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18
Q

Cmax

A

max plasma conc of drug achieved

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19
Q

drug: half-life

A

time taked for conc in plasma to fall to 1/2 original value

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20
Q

therapeutic index

A

ratio that compares the blood concentration at which a drug causes a therapeutic effect to the amount that causes death or toxicity

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21
Q

where will drugs go from the plasma

A

plasma –> ISF —> ICF (or other trancellular fluid)

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22
Q

what must drugs do to cross compartemnts and what are the 2 ways they go about this

A

Must cross barriers:
* Paracellular (filtration) - filter between cells
* Transcellular - through cells

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23
Q

3 types of barrier, and what makes them different in terms of drug absorption

A

Continous - hard for drugs to cross
Fenestrated - more holey
Sinusoid - incomplete basement membrane with intercellular gaps

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24
Q

Describe the meachanisms which drugs can use to travel from the plasma to tissues

A
  • diffusion
  • facilitated diffusion
  • active transport
  • endocytosis
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25
Q

what does the uptake of blood into tissues depend on

Key flashcard

A
  • Lipophilicity - can easily diffuse across cell membrane
  • Blood supply (perfusion) - inc blood supply, inc rate of drug delivery
  • Ion trapping? - if ionic then hard to cross capillary/cell membrane so “trapped” there
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26
Q

if drugs are lipid soluble (lipophilic) what os diffusion driven by (instead of pumps/channels etc.)

A

conc gradient

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27
Q

what are tissue compartments

A

grouping tissues that show similar conc vs time profile

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28
Q

xenobiotic

A

chemical substances that are foreign to animal life and thus includes such examples as plant constituents, drugs, pesticides, cosmetics, flavorings, fragrances, food additives, industrial chemicals and environmental pollutants

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29
Q

what is the purpose of drug metabolism

+ what are the steps

A

make the metabolite more polar than the parent compound and thus, more easily excreted

Phase 1 (functionalisation) and phase 2 (synthetic)

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30
Q

what can characteristics that facilitate absorption and diistribution do to excretion

A

inhibit it - lipophilic dugs more easily reabsorbed

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31
Q

How is the liver important in drug metabolism

A
  • Main site of metabolism/excretion
  • CYP450 = enzyme that helps with M/E
  • polymorphic variation
  • liver health impacts rate of excretion
  • Liver toxicity = inc risk of toxicity (impacts safety and efficacy)
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32
Q

briefly summarise pathway of xenobiotic to excretion

A

Xenobiotic –Phase1–> active metabolite –Phase2–> conjugate —-> Excretion

can skip 1, skip 2, do 2 then 1 or 1 then 2 or none ;)

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33
Q

biliary excretion

A

active secretion of drug molecules or their metabolites from hepatocytes into the bile

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34
Q

What are the main routs of drug administration

A
  • IV: bioavailability = 100
  • Oral (most common)
  • Subcutaneous
  • Intramuscular (IM)
  • Nasal
  • Inhaled
  • Transdermal
  • other GI (rectal, sublingual)
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35
Q

benefit of sublingual drug administration

A

bypasses first pass metabolism

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36
Q

Define each bit of ADME

A

Absorption: how a chemical enters the body. Absorption relates to the movement of a chemical from the administration site to the bloodstream.
Distribution: drug moves from the absorption site to tissues around the body via the bloodstream, but can also occur from cell-to-cell.
Metabolism: biotransformation of drug by tissues/organs so the drug can be excreted.
Excretion: the process by which the metabolized drug compound is eliminated from the body.

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37
Q

what are the mechanisms of ADME

A

normal physiological mechanisms we exploit when developing mediecations

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38
Q

bulk flow

A

the movement of fluids down a pressure or temperature gradient

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39
Q

2 important organs in drug elimination and toxicity

A

Kidney and liver

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40
Q

absorption

A

process of mass transefer from site of administration to bloodstream

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41
Q

what does the extent and rate of drug absorption depend on

A
  • physiochemical properties of the drug (e.g. size, lipophilicity, ionic…)
  • Dosage form
  • Anatomical/physiological factors
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42
Q

are all drugs absorbed

A

No, some (e.g. topical) arn’t absorbed

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43
Q

do topical drugs reach systemic circulation

A

Yes, some can

44
Q

why would we not want a drug to be absorpbed into systemic circulation

A

Only want to effect site of application (e.g. local anaesthetics)

45
Q

How do we administer local anaesthetics to avoid them reaching systemic circulation

A
  • Don’t inject into circulation
  • Avoid highly vascular tissues
  • Co-administer with adrenaline - causes vascoconstriction
46
Q

what is half -life

check

A

tiem take for Cmax to reach half value

47
Q

Factors to affect oral absorption

A
  • solubility affected by gut’s contents
  • Gastic emptying time (e.g. poo before absorpted)
  • pH change throughout gut - ionize
  • Guit flora
  • First pass metabolism
48
Q

Ficks first law of diffusion

A

the rate of diffusion of a substance across unit area (such as a surface or membrane) is proportional to the concentration gradient

49
Q

things affecting fick’s first law (diffusion)

A
  • Diffusion coefficient
  • size etc.
  • partion coefficient
  • thickness of membrane
  • membrane area
  • Drug concentration
50
Q

First order kinetics

A

occur when a constant proportion of the drug is eliminated per unit time. Rate of elimination is proportional to the amount of drug in the body. The higher the concentration, the greater the amount of drug eliminated per unit time. For every half life that passes the drug concentration is halved. - more drug in the body, the faster it is removed

51
Q

Facilitated diffusion

A

for large or lipophobic molecules?
Eventually saturable so inc dose does not inc rate of absorption

52
Q

What are some additional barrier to distribution

A

protected tissues: brain, testis, ovary, placenta

BBB

53
Q

Plasma protein binding

A
  • Happens in distribution
  • The bound portion may act as a reservoir or depot from which the drug is slowly released as the unbound form.
  • Affects drug’s half life
  • Essentialy drugs bound to protein (e.g. Albumin) and circulate in bloodstream until free drug used. Then bound drug released and cycle continues until all is used up
54
Q

free drug hypothesis

A

assumes that the unbound drug concentration in blood is the same as that in the site of action at steady state

55
Q

Is plasma protein bound drug active

A

No

56
Q

volume of distribution

A

apparent volume into which the drug is distributed to provide the same concentration as it currently is in blood plasma

Proportionality constant between the total amount of drug in the body and the amount in the plasma at any one time - total inc bound drugs and assumes instantaneous equilibration

57
Q

Drugs with low Vd

A

remain in plasma (less distribution)

58
Q

drugs with high Vd

A

leave the plasma (more distribution)

59
Q

what does drug plasma concentration drive

A

the therapeutic effect

60
Q

overall what does Vd influence

A

[plasma]

61
Q

half-life property of drugs with high Vd

A

Drugs with high Vd tend to have longer elimination half-life

62
Q

What can Vd be used to calculate

A

loading dose

63
Q

steady state

A

every time administer dose, get peaks and troughs (loading dose) until steady state achieved where have constant concentration

64
Q

con of inhaled medication

A

much is swallowed and only 5% ends up in lungs

65
Q

Apart from dose of drugs what else can we manipulate

A

Dosage form: e.g. hexamers vs monomers, fast vs long acting…

???

66
Q

medical importance of first pass metabolism

A

educe the total exposure of the body to drug

67
Q

factors to affect bioavailability

A
  • chemical composition
  • how it is administered
  • patient’s physiology
68
Q

effect of plasma protein binding on bioavailability

A

It can limit the bioavailability of active compounds by controlling their passage through biological membranes; however, binding to plasma proteins allows hydrophobic drugs to be transported in the aqueous environment of the human organism

69
Q

zero order kinetics

A

Zero-order kinetics undergo constant elimination regardless of the plasma concentration, following a linear elimination phase as the system becomes saturated.

70
Q

tmax

A

The time it takes for a drug to reach the maximum concentration (Cmax) after administration of a drug that needs to be absorbed

71
Q

AUC

A

Are under curve: area under the plot of plasma concentration of a drug versus time after dosage

72
Q

drug clearance

A

the rate at which a drug is removed from plasma(mg/min) divided by the concentration of that drug in the plasma (mg/mL).

73
Q

Specific barriers (e.g. BBB, testes, placenta, ovarie)

A

Have continouse membranes

(no fenestrations or sinezoids)

74
Q

Xenobiotics

A

compounds other than those with a well-defined physiological role

75
Q

what are endogenous compounds administered at concentrationsoutside the normal physiological range classed as

A

xenobiotics

76
Q

Ways of physical removal of drugs from body

A

urine, bile, sweat, perspiration

77
Q

Biotransformation

A

Processing of increasing polarity of molecule making it less likely to be reabsorbed: Phase 1 and Phase 2

78
Q

Biotransformatio: phase 1 reactions

A

Creating a functional group or modifying an existing one: largely oxidisation and conducted by CYP450s but could also be hydrolysis

Metabolisation

79
Q

Where does Phase 1 of biotransformation (metabolisation) occur

A

Liver (also extrahepatic activity) and in gut/small intestine/lungs/kidney

80
Q

Where in the cell is CYP450 found

A

membrane protien in mitochondria and cytosol, much in the SER

81
Q

Toxicity of Phase 1

A

small number of phase 1 metabolites are toxic: Quinones and quinone analogues

Activation of prodrugs dec toxicity

82
Q

what can be seen in cytochrome p450

A

mutations and polymorphism

83
Q

cytochrome P450 with broad substrate specificity

A

3A4

84
Q

Phase 2 biotransformation

A
  • Products less active, larger and more hydrophilic so more likely to be exreted
  • Tend to be weak ions - ion trapping
  • More likley to bind to albumin
  • Need cofactors - glucuronic acid
85
Q

food-drug interactiong with CYP450

A
  • CYP3A4 and grapefruit juice
  • Omepraxole induces CYP3A4

Polymorhic variation

86
Q

what is warfarin metabolised by

A

CYP2C9

87
Q

Drug elimination

A

final removal of drug from body. Includes metabolism and excretion

88
Q

Do drugs have to be metabolised before being excreted

A

not always

89
Q

excretion

A

rateof drug removal from body

90
Q

Define clearance

A

volume of plasma from which the drug would be totally removed per unit time

first order process

91
Q

factors to affect [drug] in plasma

A

bioavailability and clearance

92
Q

what is total clearance

A

renal + hepatic + lung… etc.

93
Q

Renal clearance includes:

3

A
  • Glomerular filtration
  • active tubular secretion
  • tubular reabsorption
94
Q

Explain the process of fibtration and the conditions which must be met

A
  • drug must be in plasma (and free)
  • Depends on Vd and protein binding as well as size and charge
95
Q

total renal clearance

maybe don’t bother learning

A

No secretion/reabsorption

96
Q

what is active renal secretion

A
  • occurs in proximal tubule
  • clears drugs too large to filter
  • depends of drug flow, free drug
  • saturable
97
Q

what + what = renal clearance

A

secretion +GFR

98
Q

passive tubular reabsorption

A

passive process whereby drugs are reabsorbed into the systemic circulation from the lumen of the distal tubules - depends on urin flow rate and pH - ion trapping

99
Q

wht is renal clearance proportional to

A

GFR

100
Q

briefly describbe hepatic clearance

A
  • perfusion important here
  • dependent on efficiency of removal of drug from blood
101
Q

what does hepatic clearnce equal

A

hepatic clearance = hepatic blood floow x hepatic extraction ratio

102
Q

Intrinsic clearance capacity

A

a measure of the maximal ability of the liver to metabolize a drug in the absence of protein binding or blood flow limitations
High: hepatic clearance is perfusion limited

103
Q

enterohepatic recirculation

A
  • poorly reabsorbed
  • enzymes expressed bu gut microbiota can de-conjugate and allow its reabsorption
  • secondary drug absorption —> prolonged drug action
104
Q

what does renal disease increase the risk of

A

drug toxicity

105
Q

how can renal disease increaseing the risk of drug toxicity be accounted for

A

by alterations in the dosing strategy

2. Foundations of Medicine PoD (28 decks)

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