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MDTI > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

definition of drug

A

a chemical entity that affects living protoplasm

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2
Q

definition of medicine

A

a chemical entity used to treat, cure, prevent, or diagnose disease

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3
Q

pharmacology definition

A

study of drugs

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4
Q

how do we achieve goal of drug therapy/medicine?

A

must get adequate amounts of the drug to tissues so that the effect of the drug can be achieved while limiting the toxicity of the drug

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5
Q

pharmacokinetics

A

describes what happens to a drug given to a patient. what the body does to the drug

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6
Q

pharmacodynamics

A

THE BODY’S RESPONSE TO A given drugs. what the drug does to the body

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7
Q

fundamentals of pharmacokinetics

A

AADME (administration, absorption, delivery, metabolism, excretion)

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8
Q

enteral drug administration

A

oral, rectal, sublingual

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9
Q

parenteral drug administration

A

IV, IM, Sub Q

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10
Q

advantages of oral administration

A

ease of use, outpatient care, low cost

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11
Q

disadvantages of oral administration

A

most complicated path and therefore most variable response, first pass effect

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12
Q

first pass effect

A

the concentration of a drug is greatly reduced before it reaches the systemic circulation (hepatic vein to IVC). It is the fraction of lost drug during the process of absorption which is generally related to the liver and gut wall

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13
Q

enteropathic circulation

A

instead of taking portal vein to liver, some drugs are recycled back and forth within GI

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14
Q

advantages of rectal administration

A

relative ease of use, outpatient care, low cost, no pH/food effects, tolerability

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15
Q

disadvantages of rectal administration

A

(less) complicated path/variable response. (less) first pass effect

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16
Q

advantages of sublingual administration

A

ease of use, outpatient care, *rapid onset of action (direct systemic absorption), bypasses stomach/intestine, *no first pass effect

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17
Q

disadvantages of sublingual administration

A

expensive, taste, limited available formulations

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18
Q

advantages of IV (IA) administration

A

bypasses stomach/intestine, no first pass effect, precise control of dose, rapid onset of action

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19
Q

disadvantages of IV (IA) administration

A

invasive (IA especially painful), expensive, unintentional overdosing, inpatient/supervised

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20
Q

advantages of IM/Sub Q administration

A

bypasses stomach/liver, aqueous solution=fast onset of action, non-aqueous solution=slow sustained response

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21
Q

disadvantages of IM/Sub Q administration

A

invasive, expensive, requires absorption, supervised, impossible to remove

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22
Q

transdermal administration

A

skin acts as rich absorptive SA, bypasses first effect, improved compliance, lipid solubility determines absorption

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23
Q

topical drug delivery

A

delivering drug directly to site of needed action

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24
Q

administration via inhalation

A

rapid delivery over large SA of respiratory tract, lung parenchyma is permeable to peptides, lower metabolism in lung tissue, molecular size must be small

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25
Q

absorption definition

A

transfer of drug from the site of administration to systemic circulation

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26
Q

which type of administration has complete absorption?

A

IV (100%)

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27
Q

what does GI absorption depend upon?

A

blood supply, presence of food in stomach, presence of other meds in stomach, level of enterocyte metabolism, disease states, permeation principles, effect of pH

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28
Q

permeation principles

A

passive diffusion, lipid diffusion, special carriers, endo/exocytosis

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29
Q

ticks law of diffusion

A

movement from high to low areas of concentration

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30
Q

how do water soluble drugs penetrate membrane via diffusion?

A

through aqueous channels. increased size diminishes absorption

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31
Q

how of lipid soluble drugs penetrate membrane via diffusion?

A

through the membrane. size isn’t an issue, but charge is

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32
Q

henderson hasselbach principle for lipid diffusion

A

tells what proportion of drug will be in uncharged state at any given pH. easier for uncharged to pass membrane so most drugs are weak acids/bases

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33
Q

where do weak acids vs bases generally get absorbed?

A

acids: stomach
bases: intestine

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34
Q

carrier mediated absorption

A

energy dependent process requiring ATP. moves drugs against concentration gradient, saturable

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35
Q

bioavailability

A

the efficiency of absorption. fraction of the administered drug that reaches the systemic circulation in an UNCHARGED form

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36
Q

calculate bioavailability

A

area under curve for administration/area under curve for IV

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37
Q

how does first effect affect bioavailability

A

reduces it since amount actually absorbed in systemic circulation is decreased by gut enterocytes and liver

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38
Q

definition of distribution

A

process by which a drug REVERSIBLY leaves the blood stream and enters the interstitial and/or cells of a tissue

39
Q

what happens once a drug distributes?

A

enters one of three compartments or is sequestered

40
Q

where are drugs most commonly sequestered?

A

bone and adipose tissue (fetus if pregnant)

41
Q

three compartments a drug can distribute into

A

plasma, interstitial fluid, intracellular fluid

42
Q

ECF

A

plasma + interstitial fluid

43
Q

total body water

A

plasma + IF + ICF =42L

44
Q

what determines where a drug distributes?

A

blood flow, capillary permeability, hydrophobicity/lipophilicity of drug, binding to plasma proteins

45
Q

blood brain barrier

A

brain capillary endothelial cells are continuous via tight junctions and prevent substances from entering interstitium

46
Q

role of plasma proteins

A

sequester drugs in a nondiffusible form in the plasma. drugs bound to them are inactive, binding is reversible though.

47
Q

volume of distribution

A

a hypothetical volume of fluid into which a drug is disseminated prior to elimination. (bioavailable dose)/(concentration in plasma)

48
Q

small Vd after drug is displaced from plasma protein binding site…

A

concentration in plasma is high=increased risk of toxicity

49
Q

large Vd after drug is displaced from plasma protein binding site…

A

drug can distribute into other compartments and risk of toxicity is low

50
Q

value of Vd if drug is distributed throughout total body water

A

0.6 L/Kg

51
Q

Large Vd tells drug is distributed…

A

throughout entire body (water soluble, easily distributed, small molecule)

52
Q

Small Vd tells drug is distributed…

A

within plasma.

53
Q

drugs only distributed in plasma

A

large molecular weight or binds tightly to plasma proteins, too big to pass into IF or not free to do so

54
Q

drugs distributed to ECF

A

low molecular weight, hydrophilic, can move through endothelial slit junctions into IF.

55
Q

drugs distributed throughout total body water

A

drug has low molecular weight, lipophilic, can move through cell membrane and slit junctions, distribute into huge volume, water soluble

56
Q

drugs distributed to tissues

A

drug bound receptors or carrier mechanism, drug sequestered in bone or fat tissue

57
Q

elimination

A

metabolism + excretion

58
Q

metabolism/biotransformation primary purpose

A

inactivate drug. achieved by converting drug into more excitable form (polar compound)

59
Q

prodrugs

A

require biotransformation to become activated

60
Q

where does the majority of drug metabolism take place?

A

liver (but really any cell with mitochondria)

61
Q

phase 1 drug metabolism

A

oxidation via cytochrom P450. primary mode of metabolism, difficult to saturate

62
Q

phase 2 drug metabolism (not always sequential)

A

couples endogenous substrate to a drug or to its phase 1 metabolite. CONJUGATION. (acetylation, methylation, etc)

63
Q

CYP

A

cytochrome P-450 system. major catalyst of drug and endogenous compound oxidations

64
Q

most common CYP families

A

1,2,3

65
Q

which specific CYP protein is responsible for many drug metabolisms

A

CYP3A4

66
Q

rifampin

A

drug used in treatment of TB. side effect=orange fluid. increases activity of CYP3A4, therefore decreasing the efficacy of drugs dependent on phase 1 (breaks them down quicker, St Johns Wort too)

67
Q

grapefruit juice

A

decreases activity of CYP3A4 in GI endothelial cells, thereby increasing timespan/concentration of dependent drugs

68
Q

polymorphisms in CYP family genes

A

increased copies of genes leads to faster metabolism of dependent drugs (CYP2D6 example)

69
Q

consequence of reduced metabolism

A

toxicity, death

70
Q

consequence of increased metabolism

A

loss of efficacy

71
Q

inhibition of gastric endothelial cell CYP3A4 activity results in…

A

increased absorption of orally administered drugs

72
Q

enterohepatic circulation

A

biliary excretion

73
Q

functional unit of the kidney

A

nephron

74
Q

three processes of renal excretion

A

glomerular filtration, active tubular secretion, passive tubular reabsorption

75
Q

amount of drug excreted by the kidney

A

the sum of the amount filtered and secreted minus the amount reabsorbed

76
Q

elimination

A

metabolism & excretion. the process whereby the body terminates drug action

77
Q

what is the rate of elimination called?

A

clearance

78
Q

what is clearance proportional to?

A

concentration of the drug

79
Q

first order kinetics

A

when clearance is DIRECTLY proportional to the concentration of the drug

80
Q

zero order kinetics

A

capacity limited excretion, elimination is saturable.

81
Q

kinetics at low drug concentrations

A

first order

82
Q

kinetics at high drug concentrations

A

zero order (saturable)

83
Q

half life of drug

A

the time required to eliminate half of the amount of drug in the body or to reduce the plasma concentration by 50%

84
Q

how is half life of drug calculated?

A

from the plasma concentration curve following administration of a single dose of the drug

85
Q

how many half lives for first order kinetics to eliminate >90% of drug?

A

4

86
Q

steady state concentration

A

when rate of accumulation is equal to the rate of elimination

87
Q

how long does it take to reach steady state?

A

4-5 half lives (think inverse of elimination: i.e. how long to reach >90%/plateau)

88
Q

what is the steady state concentration directly proportional to?

A

drug dose administered per unit of time and the elimination half life

89
Q

will a drug administered by continuous infusion reach steady state at different time than drug administered intermittently?

A

no, they will both reach it at the same time, but intermittent drug plasma level will just flucuate

90
Q

loading dose

A

a dose that saturates. used when it is necessary to rapidly achieve a therapeutic plasma concentration. commonly used with antibiotics and anticoagulants

91
Q

maintenance dose

A

given to establish or maintain a desired steady state concentration

92
Q

impact of liver disease on pharmacokinetics

A

reduced phase 1 metabolism and reduced albumin

93
Q

impact of renal failure on pharmacokinetics

A

reduced GFR and secretion

94
Q

impact of heart failure on pharmacokinetics

A

volume expansion, reduced circulation

MDTI (42 decks)

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