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Pharm > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

pharmacokinetics (3)

A

absorption
distribution
elimination

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2
Q

IV meds vs PO meds

A

IV onset of action is immediate. Tmax is immediate. PO is not because it had to travel through multiple different organ systems before systemic circulation.

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3
Q

Bioavailability

A

the fraction of an administered dose of drug that reaches the systemic circulation unchanged

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4
Q

bioavailability % of PO meds vs IV meds

A

PO meds <1 or <100% (typically 15-95%), IV meds 1 or 100%

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5
Q

factors that affect PO bioavailability (4)

A
  1. solubility/ability of drug to resist breakdown in stomach
  2. ability of drug to permeate and resist metabolism in the GI epithelium
  3. ability of drug to resist metabolism in portal circulation
  4. ability of drug to resist metabolism within the liver, hepatic vein, lungs, etc.
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6
Q

first pass effect

A

when the concentration of a med is greatly reduced before entering systemic circulation. typically PO meds.

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7
Q

process of first pass effect

A

PO meds are absorbed in GI tract and circulated to liver via hepatic portal vein. liver metabolizes part of the med before it reaches systemic circulation. this combination results in first pass effect.

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8
Q

factors affecting distribution from plasma: endothelial cell fenestration

A

a high degree of fenestration, like in the liver and kidney, facilitates more distribution. low degree of fenestration, like in the brain, prevents distribution.

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9
Q

factors affecting distribution from plasma: blood flow

A

high blood flow like in major organ systems facilitates distribution. low blood flow, like in joints or fat or bones, leads to less distribution.

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10
Q

factors affecting distribution from plasma: lipophilicity and molecular weight

A

lipophilic drugs will pass through the membrane much easier, as will drugs with a lower molecular weight.

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11
Q

factors affecting distribution from plasma: protein bound

A

protein bound meds will have a harder time crossing the cell membrane.

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12
Q

factors affecting distribution from plasma: ionization

A

uncharged passes easier.

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13
Q

blood brain barrier purpose and components

A

the barrier that protects the CNS from outside medications. this is achieved through low fenestration, encapsulated cells, efflux transporters on the barrier (pgp transporter).

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14
Q

ion trapping

A

distribution of meds based on pH

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15
Q

if a drug is a weak acid…

A

it will want to go toward a more basic environment (plasma).

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16
Q

if a med is a weak base…

A

it will want to go towards a more acidic environment (neurons)

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17
Q

volume of distribution. what is it and what is the equation?

A

it is a proportionality constant.
equation is
amount of drug in the body divided by the concentration of drug in plasma.

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18
Q

Vd < 5 L

A

most of med is confined to plasma

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19
Q

Vd is between 5 - 10 L

A

medication is distributed throughout the blood

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20
Q

Vd > 42 L

A

med is distributed to all tissues in the body

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21
Q

protein bound drugs remain in

A

the bloodstream

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22
Q

drug elimination

A

irreversible removal of medication from the body

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23
Q

two categories of elimination

A

metabolism and excretion

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24
Q

drug metabolism

A

the enzymatic conversion of a medication to its metabolites

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25
Q

drug excretion

A

the removal of unchanged medication from the body

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26
Q

phase I reactions

A

anything that goes through cytochrome p450 or a cyp enzyme
oxidation
reduction
hydrolysis

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27
Q

phase II reactions (5)

A 
glucuronidation
sulfation
acetylation
peptide conjugation
glutathione conjugation
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28
Q

phase 1 and phase 2

A

meds may go through none, one, or both.

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29
Q

cytochrome p450 and CYP enzymes are largely found in

A

the liver

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30
Q

active parent compound

A

active from ingestion to metabolism from liver, then metabolized into inactive metabolites.

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31
Q

prodrug

A

the med is inactive UNTIL it is metabolized by the liver. when metabolized, the med is transformed into an active metabolite which exhibits the therapeutic effect.

32
Q

metabolism of acetaminophen

A

goes through both phase I and phase II
CYP mediated reaction (phase I) and then sulfation
and glutathione conjugations (phase II).
After CYP mediated reaction, you have NAPQI. This is a toxic metabolite and needs to be converted and eliminated. This is where you need a glutathione conjugation (phase II) to convert NAPQI into a less toxic metabolite.

33
Q

acetaminophen toxicity

A

if you can’t go through the steps of metabolizing acetaminophen. after acetaminophen is metabolized through phase I and II, phase I converts acetaminophen into NAPQI. Glutathione has to then conjugate the NAPQI because it’s toxic. if not, you’ll have serious AEs like hepatocyte death.

34
Q

purpose of acetylcystine

A

in acetaminophen overdose….provides your body with glutathione to break down NAPQI.

35
Q

Half life

A

parameter defined by the time it takes for the concentration of a med to reach half of its present concentration

36
Q

what can half life be used to determine?

A

how long a med will last in the body.

37
Q

how many half lives to steady state?

A

~ 4 - 5

38
Q

How many half lives to ~99% drug removal?

A

5 half lives.

39
Q

First order kinetics

A

constant elimination of med per unit of time, proportional to amount of med in the body. same proportion is eliminated per unit of time, meaning the amount is variable based on plasma conc. as the conc drops, the elimination rate drops as well.

40
Q

zero order kinetics

A

constant elimination of med in mg/hr, regardless of amount of med in body. the same amount is eliminated per unit of time regardless of plasma concentration.

41
Q

elimination mechanism is saturated in ____ order kinetics

A

zero

42
Q

phenytoin elimination and considerations.

A

follows zero order kinetics.
as you dose pts, you will reach a point where all receptor sites are saturated. elimination continues at same fixed rate but an increase in therapeutic effect will be seen bc of buildup of the med waiting to bind as receptors desaturate. As you get to higher concentrationss, even small changes can have big impact on therapeutic effects.

43
Q

clearance (CL) equation

A

the rate of elimination of a drug divided by the plasma concentration of a drug

44
Q

clearance equation

A

clearance in L/hr = elimination in mg/hr OVER concentration in mg/L

45
Q

rate of elimination

A

clearance x concentration

46
Q

steady state definition

A

rate of absorption is equal to the rate of elimination of given med

47
Q

dosing rate equation

A

clearance x steady state conc

48
Q

creatinine clearance

A

measurement used to determine level of kidney function by looking at how well your kidneys are clearing creatinine from the blood.

49
Q

creatinine clearance Cockcroft-gault equation

A

creat clearance ml/min = (140-age) x weight in kg OVER serum creatinine mg/dl x 72 ALL MULTIPLIED BY 0.85 if female

50
Q

at what creatinine clearance do you need to make renal adjustments?

A

below 30 or 40.

51
Q

drug-drug interactions at pharmacokinetic level can happen during what 4 stages?

A

absorption, distribution, metabolism, excretion

52
Q

what happens when there is a drug-drug interaction between two drugs metabolized by the same enzyme

A

competition between the two drugs for the enzyme to metabolize them. the one that loses out on being metabolized will have high concentrations of free drug.

53
Q

drug-drug interactions: GI absorption (3 points)

A
  • absorption of other drugs can be delayed by drugs that inhibit gastric emptying, like opiates
  • absorption of other drugs can be increased by drugs that speed up gastric emptying, like erythromycin.
  • absorption can be slowed or completely inhibited by formation of physical complexes (iron and tetracyclines)
54
Q

drug-drug interactions at the level of distribution is typically related to

A

protein binding drugs and albumin

55
Q

hypoalbuminemia and protein bound drugs

A

increased concentrations of free drug in circulation bc less protein is available to bind to. increased clinical effect/potential side effects. not guaranteed to be a problem.

56
Q

changes in hepatic metabolism are a common cause of

A

drug-drug interactions

57
Q

2 factors that affect hepatic metabolism in the context of drug-drug interactions

A

enzyme inhibition

enzyme induction

58
Q

when analyzing enzyme inhibition/induction interactions, it is important to know what about a drug?

A

if it is an APC or a prodrug

59
Q

enzyme inhibition

A

occurs when a medication reduces the activity of a metabolic enzyme, decreasing its metabolic capacity.

60
Q

enzyme induction

A

occurs when a med enhances a metabolic enzyme, increasing its activity.

61
Q

if a med is an inducer of a CYP3A4 enzyme and another med, normally metabolized by CYP3a4 is given, what will happen?

A

it will be metabolized faster

62
Q

if an APC med metabolized by CYP3A4 is given with a med which induces CYP3a4, what will you expect?

A

the APC will be converted into an inactive metabolite at a faster rate. less of a clinical effect will be seen.

63
Q

if a prodrug, normally metabolized by CYP3A4, is given with a med that induces CYP3a4, what will you expect?

A

the prodrug will be converted to an active metabolite quicker and a greater clinical effect will be seen.

64
Q

if you have a med that inhibits CYP3A4 and then an APC given that is metabolized by cyp3a4, you should expect

A

a greater clinical effect/concentration because the APC will not be metabolized into an inactive metabolite as quickly. the active form of the drug will remain active for longer.

65
Q

if you have a med that inhibits CYP3A4 and a prodrug metabolized by CYP3A4, what will you expect?

A

diminished effect. the inactive drug will not be metabolized into its active metabolite at the rate it normally would.

66
Q

atorvastatin is a prodrug and CYP3A4 substrate. ketoconazole is a moderate inhibitor of CYP3A4. give them together - what is the expected outcome?

A

moderately diminished effect. inactive parent form would not be metabolized into its active metabolite as it normally would be.

67
Q

diltiazem is an APC and known substrate of CYP3A4. St John’s Wort is a CYP3A4 inducer. Give them together - what do you expect?

A

diltiazem would have a diminished effect because its active parent compound would be metabolized quickly

68
Q

absorption of medications is based on

A

route of administration

69
Q

volume of distribution is a

A

proportionality constant

70
Q

which meds cross membranes easier? protein bound or free/unbound form?

A

free/unbound

71
Q

CYP enzymes are

A

hepatic enzymes responsible for drug metabolism of many meds

72
Q

measuring the clearance of a med gives insight on

A

how well an organ is functioning

73
Q

equation for volume of distribution

A

Vd = amount in body at equlib OVER conc in plasma

74
Q

Cmax

A

dose concentration that dose achieves

75
Q

Tmax

A

time is takes to reach Cmax

Pharm (31 decks)

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