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pharmacokinetics Flashcards

1
Q

drug has Vd of .35mL/kg. in 70kg patient, what IV loading dose must be administered to achieve a plasma concentration of 8mg/dL

A

196mg
(.35L/kg x 70 = 24.5L)
(24.5L x 8mg/L) / 1 =
loading dose = (Vd x desired CP) / bioavailability

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2
Q

Vd=

A

amount of drug/desired plasma concentration

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3
Q

Vd assumes two things

A
  1. drug distributes instantaneously (full equilibration occurs at time =0)
  2. Drug is not subjected to biotransformation or elimination before it fully distributes
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4
Q

review distribution of body water in 70kg patient
tbw
extracellular (plasma volume, ISF)
intracellular

A
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5
Q

lipophilic drug characteristics

A

Vd exceeds TBW (>.6L/kg or >42L)
distributes into TBW and fat
requires higher dose to achieve plasma concentration

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6
Q

hydrophilic drug characteristics

A

Vd less than TBW (<.6L/kg or <42L)
distributes into some or all of body water but not fat
require lower dose to achieve given plasma concentration

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7
Q

Vd is affected by which 2 characteristics

A

drug (molecular size, ionization, protein binding)
patient (pregnancy and burns)

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8
Q

loading dose=

A

Vd x (desired plasma concentration/ bio availability)
IV: bio availability =1

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9
Q

clearance is directly proportional to (3)

A

blood flow to clearing organ
extraction ratio
drug dose

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10
Q

clearance is inversely proportional to (2)

A

half life
drug concentration in central compartment

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11
Q

review this graph

A

alpha: redistribution- steepest part of curve
beta: elimination from central compartment- less steep part of curve
A+B represents plasma concentration over time

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12
Q

k12

A

rate constant for drug transfer from central compartment to peripheral compartment

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13
Q

k21

A

rate constant for drug transfer from peripheral compartment to central compartment

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14
Q

ke

A

rate constant for drug elimination from body

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15
Q

describe three compartment model

A

different rate constants going to and from each compartment.

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16
Q

elimination half life versus elimination half time

A

time it takes for 50% of drug to be removed after rapid IV injection versus

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

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17
Q

amount of drug eliminated and half times

A

drug is considered eliminated after 96.9% is gone

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18
Q

half time measures what

A

constant fraction and not constant amount

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19
Q

define context sensitive half time

A

time required for plasma concentration to fall by 50% after the infusion is stopped

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20
Q

review the context sensitive half time graph as it relates to phenylpiperdines

A
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21
Q

an acid _______ a proton while a base ________ a proton

A

acid: donates a proton
base: accepts a proton

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22
Q

ionization is dependent on two things

A

pH of solution and pKa of drug

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23
Q

pKa =

A

pH where 50% of drug is ionized and 50% is non ionized

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24
Q

henderson hasslebach equation

A

pH= pKa + log (base/conjugate acid)

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25
Q

weak bases in an acidic versus basic solution

A

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

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26
Q

weak acids in acidic versus 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

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27
Q

a drug that is a weak acid is paired with

A

a positive ion such as sodium, calcium, or magnesium

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28
Q

a drug that is a weak base is paired with

A

a negative ion such as chloride or sulfate

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29
Q

what LA is most likely to undergo fetal ion trapping

A

lidocaine. (maternal alkalosis and fetal acidosis)

30
Q

percent change of drug bound by plasma protein

A

percent change = ((new value- old value)/old value) x 100
(96-98)/96 x 100 = 100% increase in un bound
initial: 98% bound
then: 96% bound

31
Q

albumin key facts

A

most plentiful plasma protein
primary determinant of plasma oncotic pressure
t1/2 3 weeks
carries a negative charge
primarily binds with acidic drugs
also binds with neutral and basic drugs

32
Q

what decreases Cp (plasma clearance) of drugs that bind to albumin (5)

A

liver disease
renal disease
old age
malnutrition
pregnancy

33
Q

what kind of drugs that a1 acid glycoprotein bind to

A

acidic

34
Q

plasma clearance of drugs that bind to a1 acid glycoproein are decreased by

A

neonates and pregnancy

35
Q

plasma clearance of drugs that bind to a1 acid glycoproein are increased by

A

surgical stress
MI
chronic pain
RA
advanced age

36
Q

what kind of drugs do beta globulin proteins bind to

A

acidic

37
Q

plasma clearance of drugs that bind to beta globulins are increased or decreased by

A

n/a

38
Q

zero order kinetics versus first order kineticcs

A

zero: constant amount of drug is metabolized per unit of time
first: constant fraction of drug is metabolized per unit of time

39
Q

what kind of metabolism does this represent

A

zero order kinetics
(more drug than enzyme)

40
Q

what kind of metabolism does this represent

A

first order kinetics
(less drug than enzyme)

41
Q

3 phases of drug metabolism

A

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

42
Q

phase 1: modification
biotransformation is carried out by
what happens during 3 reactions

A

increases polarity
biotransformation via p450 system
oxidation: removes electrons from compound
reduction: adds electrons to a compound
hydrolysis: adds water to a compound to split it apart (usually an ester)

43
Q

phase 2: conjugation

A

adds on endogenous, highly polar, water soluble substrate to the molecule. produces a water soluble biologically inactive molecule ready for excretion
some drugs do not need phase 1 and go directly to this

44
Q

substrates used for phase 2 conjugation

A

glucoronic acid
glycine
acetic acid
sulfuric acid
methyl group

45
Q

describe enterohepatic circulation

A

some conjugates compounds are excreted in the bile, reactivated in the intestine, and then reabsorbed into systemic circulation. usually has long effects
ex) diazepam, warfarin

46
Q

phase 3: elimination

A

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

47
Q

extraction ratio of 1

A

100% of the drug delivered to the clearing organ is removed

48
Q

extraction ratio of .5

A

means 50% of the drug delivered to the clearing organ is removed.

49
Q

a perfusion dependent elimination has an extraction ratio of______ and clearance is dependent on ____________________________

A

> .7
clearance is dependent on liver blood flow. increased liver BF, increased clearance

50
Q

a capacity dependent elimination has an extraction ratio of ______ and clearance is dependent on ______________________________

A

<.3
clearance is dependent on changes in hepatic enzyme activity or protein binding
enzyme induction increases clearance
enzyme inhibition decreases clearance

51
Q

drugs that have low hepatic extraction ratios

A

rocuronium
diazepam
lorazepam
methadone
thiopental
theophylline
phenytoin

52
Q

drugs that have intermediate hepatic extraction ratios

A

midazolam
vecuronium
alfentanil
methohexital

53
Q

drugs that have high hepatic extraction ratios

A

fentanyl
sufentanil
morphine
meperidine
naloxone
ketamine
propofol
lidocaine
bupivicaine
metoprolol
propanolol
alprenolol
nifedipine
diazepam
verapamil

54
Q

examples of enzyme inducers include

A

tobacco smoke
barrbiturates
ethanol
phenytoin
rifampin
carbamazepine

55
Q

examples of enzyme inhibitors include

A

grapefruit juice
cimetidine
omeprazole
isoniazid
SSRI’s
erythromycin
ketoconazole

56
Q

drugs metabolized via CYP3A4

A

opioids: fentanyl, alfentanil, sufentanil, methadone
benzos: midaz, diazepam
LA’s: bupiv, ropiv

57
Q

drugs metabolized by CYP2D6

A

codeine –>morphine
oxycodone
hydrocodone

58
Q

drugs metabolized by CYP1A2

A

theophylline

59
Q

lipophilic drugs that do not undergo bio transformation have what fate in the renal system

A

reabsorbed in peritubular fluid via diffusion

60
Q

two processes that deliver drug to the urine

A
  1. GFR: only free fraction unbound drug is filtered at glomerulus
  2. organic anion (OAT) and cation (OCT) transporters:
61
Q

drugs that utilize OAT

A

furosemide, thiazide diuretics, PCN

62
Q

drugs that utilize OCT

A

morphine, meperidine, dopamine

63
Q

acidic urine and drug excretion

A

favors reabsorption of acidic drugs
excretion of basic drugs
AAA- acidic drugs are better absorbed in acidic medium

64
Q

alkalotic urine and drug excretion

A

favors reabsorption of basic drugs
excretion of acidic drugs
BBB- basic drugs are better absorbed in a basic medium

65
Q

how to help acidify the urine to help eliminate basic drugs

A

ammonium chloride or cranberry juice

66
Q

how to help alkalize urine to help eliminate acidic drugs

A

sodium bicarb or acetazolamide

67
Q

drugs metabolized by nonspecific plasma esterases (6)

A

esmolol, remifentanil, atracurium, remimazolam, etomidate, clevidipine

68
Q

which drug utilizes alkaline phosphatase for metabolism/elimination

A

fospropofol

69
Q

drugs metabolized by pseudocholinesterases

A

succ, cocaine, mivacurium, ester LA’s

70
Q

drugs metabolized via hoffman elimination

A

ciisatracurium
atracurium(+ non specific plasma esterases)

71
Q

peusdocholinesterase deficiency extends DOA of

A

succ
mivacurium
cocaine
ester LA’s

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