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Apex > Unit 4 Pharmacology: Pharmacokinetics > Flashcards

Unit 4 Pharmacology: Pharmacokinetics Flashcards

1
Q

What relationship does Vd describe

A

the one between an administered dose of a drug and the plasma concentration that results

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2
Q

Vd assumes two things

A

the drug distributes instantaneously (full equilibration occurs at time =0) and that the drug is not subject to biotransformation or elimination before it fully distributes

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3
Q

what is the equation for Vd in relation to amount of drug and desired plasma concentration

A

Vd= (amount of drug/desired plasma concentration)

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4
Q

Distribution of total body water in 70kg patient:

A

ICF 28L, ECF 14L (Plasma volume 4L, ISF 10L)

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5
Q

what makes up ECF

A

plasma volume and ISF

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6
Q

when is a drug assumed to be lipophilic

A

when Vd exceeds TBW >.6L/kg (or >42L in 70k person)

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7
Q

when is a drug assumed to be hydrophillic

A

when Vd is less than TBW <.6L/kg (or <42L in 70kg person)

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8
Q

Vd is affected by which drug characteristics

A

molecular size, ionization, protein binding

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9
Q

Vd is affected by which patient characteristics

A

pregnancy and burns (among other things)

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10
Q

what is the relationship between Vd and loading dose

A

the higher the Vd, the higher the loading dose that must be given to achieve predetermined plasma concentration

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11
Q

formula for calculation of loading dose

A

Vd*(desired plasma concentration/bioavailability)

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12
Q

what is the bioavailability of an IV med

A

1, since it is injected directly into the bloodstream

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13
Q

drug clearance

A

volume of plasma that is cleared of drug per unit of time

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14
Q

clearance is directly proportional to

A

blood flow clearing organ, drug dose and extraction ratio

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15
Q

clearance is inversely proportional to

A

half life and drug concentration in the central compartment

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16
Q

most important organs involved in clearance

A

liver, kidney, organ independent (hofmann elimination and ester hydrolysis in the plasma)

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17
Q

to maintain a steady state concentration or “stable concentration” in the plasma, the infusion rate or dosing interval must equal

A

the rate of drug clearance by metabolism and elimination
(rate of administration=rate of elimination)

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18
Q

steady state is achieved after how many half lives

A

five (96.9% eliminated)

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19
Q

if a drug has a long half life, you can achieve steady state faster by

A

administering a loading dose

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20
Q

what does the plasma concentration curve illustrate

A

biphasic decrease of a drugs plasma concentration after a rapid IV bolus

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21
Q

what does the alpha phase of the plasma concentration curve illustrate

A

distribution

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22
Q

what does the beta phase of the plasma concentration curve illustrate

A

elimination

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23
Q

what is the steepness of the plasma concentration slope influenced by

A

the lipophilicity. the more lipophilic the drug, the larger the Vd, and the greater the slope

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24
Q

what is redistribution of a drug based on

A

concentration gradient between plasma and tissues (influenced by degree of lipophilicity)

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25
Q

as the plasma concentration (Cp) continues to decline as a result of continued elimination, what happens to the concentration gradient

A

it reverses and the drug redistributes back from the peripheral compartment into the central compartment

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26
Q

define rate constant

A

speed at which reaction occurs (how fast a molecule moves between compartments)

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27
Q

define K12

A

rate constant for drug transfer from central to peripheral compartment

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28
Q

define K21

A

rate constant for drug transfer from peripheral to central compartment

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29
Q

define ke

A

rate constant for drug elimination from the body

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30
Q

what is the big takeaway from a three compartment model (as compared to the two compartment model we use at baseline)

A

there are different rate constants to and from each compartment and from the central compartment. and some compartments may saturate before others. so different rates of compartment saturation impact how the drug is eliminated from the body

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31
Q

after administering an IV drug that distributes into a one compartment model, the patients serum contains 6.25% of the original dose. how many half lives have elapsed?

A

4

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32
Q

elimination half life

A

the time it takes for 50% of the drug to be removed from the body after rapid IV injection

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33
Q

elimination half time

A

the time it takes for 50% of the drug to be removed from the plasma during the elimination phase

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34
Q

when will the elimination half life and elimination half time be different

A

when the rate of drug removal from the plasma is not the same as the rate of drug removal from the body

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35
Q

does half life measure a constant fraction or a constant amount?

A

constant fraction. ex) it takes the same time for the plasma concentration of a drug to fall from 200mg/L to 100mg/L as it takes for the same drug to fall from 50mg/L to 25mg/L

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36
Q

define context sensitive half time

A

time required for plasma concentration to decline by 50% after the infusion has stopped. it takes the duration of drug administration into account

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37
Q

context sensitive half time of phenylpiperdines from highest to lowest

A

fentanyl (by far), alfentanil, sufentanil, remifentanil

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38
Q

define an acid

A

substance that donates a proton HA+<–>H+ + A
(a drug that is a weak acid will donate a proton to water)

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39
Q

define a base

A

substance that accepts a proton B- + H+ <–> BH
(a drug that is a weak base will accept a proton from water)

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40
Q

what’s the difference between a strong base or acid and a weak base or acid?

A

if you put a strong acid or a strong base in water, it will dissociate completely. if you put a weak acid or a weak base in water, a fraction will ionize, and the remaining fraction will be non ionized.

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41
Q

ionization is dependent on two factors

A

the pH of the solution and the pKa of the drug

42
Q

the pKa (a constant value) tells us how much the drug wants to behave like _______

A

an acid. low pKa = amazing acid. high pKa= terrible acid.

43
Q

a drugs pKa equals the pH where

A

50% of the drug is ionized and the other 50% of the drug is non ionized

44
Q

Henderson Hasslebach equation

A

pH = pKa + log ((base)/(conjugate acid))

45
Q

the bottom line about weak bases in an acidic or basic solution

A

in an acidic solution, weak bases are more ionized and water soluble
in a basic solution, weak bases are more non ionized and lipid soluble

46
Q

the bottom line about weak acids an an acidic or basic solution

A

in an acidic solution, weak acids are more non ionized and lipid soluble
in a basic solution, weak acids are more ionized and water soluble

47
Q

drug formulations: a drug that is a weak acid is usually paired with

A

a positive ion such as sodium, calcium, or magnesium
ex) sodium thiopental

48
Q

drug formulations: a drug that is a weak base is usually paired with

A

a negative ion, such as chloride or sulfate
ex) lidocaine hydrochloride

49
Q

solubility of an ionized solution

A

hydrophilic, lipophobic

50
Q

pharmacologic effect of an ionized solution

A

not active

51
Q

hepatic biotransformation of an ionized solution

A

more likely

52
Q

diffusion across lipid bilayers (BBB, GI, placenta) of an ionized solution

A

NO diffusion

53
Q

solubility of a non ionized solution

A

lipophilic, hydrophobic

54
Q

pharmacologic effect of a non ionized solution

A

active

55
Q

hepatic biotransformation of a non ionized solution

A

more likely

56
Q

renal elimination of a non ionized solution

A

less likely

57
Q

diffusion across lipid bilayer of a non ionized solution (BBB, GI, placenta)

A

yes, diffusion occurs

58
Q

when does the ionized fraction predominate

A

the molecule is a weak base and the pH of the solution <the pKa of the drug (a base is added to an acidic solution)
the molecule is a weak acid and the pH of the solution > the pKa of the drug (an acid is added to a basic solution)

59
Q

when does the non ionized fraction predominate

A

the molecule is a weak base, and the pH of the solution is > the pKa of the drug (a base is added to a basic solution)
the molecule is a weak acid, and the pH of the solution is < the pKa of the drug (an acid is added to an acidic solution)

60
Q

why does maternal alkalosis and fetal acidosis create the strongest gradient for passage of local anesthetic from the mother to the fetus?

A

maternal alkalosis increases the non ionized fraction in the maternal circulation; more LA is available to diffuse across the placenta. fetal acidosis increases the ionized fraction in side the fetus. this prevents the LA from crossing the placenta back to the mother, thus trapping it in the fetus.

61
Q

which LA is most likely to undergo fetal ion trapping

A

lidocaine

62
Q

which LA is least likely to undergo fetal ion trapping

A

chlorpromazine (due to high pKa and rapid metabolism in the mothers blood)

63
Q

how does fetal pH compare to maternal pH

A

fetal pH is a little lower

64
Q

how to calculate free fraction perfect change based on bound fraction (originally 98% bound, decreased to 96% bound)

A

percent change = [(new value of unbound - old value of unbound drug) / (old value of unbound drug)] * 100
ex) [(4-2) / 2] x 100 = 100%

65
Q

which organ synthesizes plasma proteins

A

liver

66
Q

types of weak bonds drug and protein can form (3)

A

ionic(-), hydrogen(-) or van der waals

67
Q

what does plasma protein effect (2)

A

intensity of drug effect and drug DOA

68
Q

plasma concentration of albumin can be decreased by (5)

A

liver disease, renal disease, old age, malnutrition, pregnancy

69
Q

what charge does albumin carry

A

negative

70
Q

what drugs does albumin primarily bind do

A

acidic primarily (but can sometimes bind with neutral and basic drugs)

71
Q

what drugs does a1 acid glycoprotein bind to

A

basic drugs

72
Q

plasma concentration of a1 glycoprotein is increased by (5)

A

surgical stress, MI, chronic pain, RA, advanced age

73
Q

plasma concentration of a1 acid glycoprotein is decreased by

A

neonates, pregnancy

74
Q

what drugs does the beta globulin protein bind to primarily

A

basic drugs

75
Q

why does renal disease decrease plasma protein

A

increase in protein extraction

76
Q

relationship between unbound fraction of drug and potency

A

increase in unbound fraction of drug means increase in potency

77
Q

relationship between Vd and degree of plasma protein binding

A

the volume of distribution is inversely related to the degree of plasma protein binding

78
Q

highly protein bound drugs’ metabolism and elimination rates are usually

A

slower

79
Q

zero order kinetics

A

process that metabolizes constant amount of drug per unit of time (theres not enough enzyme available to metabolize all the drug that is delivered to it aka the process is saturated. therefore, the enzyme will metabolize a constant amount per unit time.)

80
Q

first order kinetics

A

constant fraction of the drug is metabolized per unit of time (less drug than enzyme aka no saturation. most drugs we administer follow this)

81
Q

rate of metabolism depends on two factors

A

concentration of drug at site of metabolism and intrinsic rate of metabolic process

82
Q

what is concentration of a drug at the site of metabolism influenced by

A

blood flow to the site of metabolism

83
Q

what is the intrinsic rate of the metabolic process influenced by

A

genetics, enzyme induction, enzyme inhibition

84
Q

examples of drugs that utilize zero order kinetics (6)

A

ASA, phenytoin, alcohol, warfarin, heparin, theophylline

85
Q

three phases of drug metabolism

A

phase 1: modification (oxidation, reduction, hydrolysis)
phase 2: conjugation
phase 3: excretion

86
Q

types of metabolism that occur in the plasma include

A

hofmann elimination (pH and temperature dependent)
hydrolysis reactions catalyzed by non specific plasma esterase’s and pseudocholinesterases

87
Q

primary role of metabolism

A

change a lipid soluble, pharmacologically active compound into a water soluble, pharmacologically inactive byproduct

88
Q

what happens during phase 1 of metabolism

A

increase in water solubility or polarity, usually by P450 system

89
Q

what are the three types of phase 1 reactions

A

oxidation, reduction, hydrolysis

90
Q

what happens during oxidation

A

removes electrons from a compound

91
Q

what happens during reduction

A

adds electrons to a compound

92
Q

what happens during hydrolysis

A

adds water to a compound to split it apart

93
Q

what happens during phase 2 of metabolism (conjugation)

A

adds endogenous, highly polar, water soluble substrate to the molecule. produces a water soluble biologically inactive molecule ready for excretion

94
Q

common substrates for conjugation reactions (5)

A

glucoronic acid, glyceine, acetic acid, sulfuric acid, or a methyl group.

95
Q

what happens during phase 3 of metabolism (elimination)

A

involves ATP dependent carrier proteins that transport drugs across cell membranes. these are present in kidneys, liver, and GI tract

96
Q

drugs that undergo perfusion dependent hepatic elimination include

A

fentanyl, lidocaine, propofol

97
Q

drugs that undergo capacity dependent elimination include

A

diazepam and rocuronium

98
Q

hepatic clearance is dependent on

A

liver blood flow and hepatic extraction ratio

99
Q

define hepatic extraction ratio

A

how much drug is delivered to the clearing organ versus how much drug is eliminated by that organ

100
Q

hepatic extraction ratio equation

A

extraction ratio= (arterial concentration-venous concentration)/(arterial concentration)

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