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Pharmacology > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

what can leave the blood stream to go to the site of action?

A

free drug

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2
Q

what are the mechanisms of membrane penetration?

A
  1. passive diffusion
  2. carrier mediated transport - facilitated diffusion, active transport
  3. filtration
  4. Transcytosis
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3
Q

what does the henderson-hasselbalch’s equation determine?

A

extent of ionization

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4
Q

what is the henderson-hasselbalch equation for acidic drug and basic drug?

A
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5
Q

how are weak acids ionized?

A

donating proton

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6
Q

how are weak bases ionized?

A

accepting protons

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7
Q

In a low pH environment which is hard and easy to ionize? (acid or base)

A

easy - base
hard - acid

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8
Q

In a high pH environment which is hard and easy to ionize? (acid or base)

A

easy - acid
hard - base

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9
Q

which kind of drug in an acidic medium will be rapidly absorbed?

A

weak acid
less ionized -> more lipid soluble -> rapidly absorbed

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10
Q

what kind of drug in a basic medium will be rapidly absorbed?

A

weak base
less ionized -> rapidly absorbed

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11
Q

what will happen if a weak basic drug diffuses into an acidic medium?

A

will become ionized and accumulate in the environment

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12
Q

what happens with strong acids and strong bases in any kind of medium?

A

always ionized in body -> not lipid soluble -> cannot penetrate membranes by passive diffusion

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13
Q

How is a non-ionized weak acid distributed between compartments with different pH?

A

conc. same on both sides because it is freely diffusible

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14
Q

How is a ionized weak acid distributed between compartments with different pH?

A

depends on pH and pKa

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15
Q

How is the total concentration of a weak acid distributed between compartments with different pH calculated on each side?

A

sum of concentration of ionized and non-ionized form of drug

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16
Q

what is ion trapping?

A

acids accumulated in basic environment
bases accumulated in acidic environment

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17
Q

How does the urine become more acidic in drug excretion? What does this eliminate more of?

A

ammonium chloride increases -> the elimination of bases

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18
Q

How does the urine become more basic in drug excretion? What does this eliminate more of?

A

sodium bicarbonate increases -> the elimination of acids

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19
Q

what is P-gp? what does it do?

A
  • Permeability glycoprotein (P-glycoprotein)
  • uses ATP to pump out a wide variety of substrates across extra and intracellular membranes
  • DRUG EFFLUX
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20
Q

what are the other names for P-gp?

A

MDRI or ABCBI

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21
Q

where is P-gp found?

A
  • extensively distributed
  • intestinal mucosa, hepatocytes, renal PT cells, adrenal gland, and capillary endothelial cells (compromising blood-brain barrier)
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22
Q

Define absorption

A

how drug enters body fluids and distributes throughout organism

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23
Q

what are the factors that modify absorption

A

solubility, dissolution, concentration, BF, absorbing surface, pH, contact time

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24
Q

Define bioavailability

A

amount of active drug available at site of action
variable = F

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25
Q

what type of drugs have a bioavailability of 100%

A

IV

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26
Q

Relationship between IV and oral administration of same drug

A

DoseIV = DosePO x F

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27
Q

what is the bioavailability affected by?

A
  • decomposition/inactivation of drugs in intestine
  • degree of absorption
  • metabolism in wall of gut or liver
  • transport of drug by P-gp back into lumen of gut
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28
Q

Define first-pass effect

A

initial metabolism of drug while passing through wall of gut and liver

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29
Q

what is the most common, convenient, and economical method of drug administration?

A

oral

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30
Q

what are disadvantages of oral medications?

A

-irritation to intestinal mucosa, emesis
-destruction of drugs by enzymes or low pH
-irregularities in absorption
-metabolism by intestinal flora
-absorbed drug exposed to liver
-gastric emptying time
-binding to food

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31
Q

what are the advantages and disadvantages for slow release formulation?

A

-slow, uniform absorption of drug for several hours
-absorption often irregular and erratic

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32
Q

when are drugs given parenteral?

A

when drugs cannot be given by enteral route

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33
Q

what are parental routes

A

IV, IM, SubQ, intraperitoneal, intraarterial, epidural

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34
Q

Define parenteral

A

outside the intestines

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35
Q

When is inhalation used for drugs?

A

gaseous anesthetics, aerosols, rapid absorption

36
Q

where can topical drugs be applied?

A

skin, eye, nose, throat

37
Q

Does topical drugs achieve local or systemic absorption?

A

systemic

38
Q

what conditions affect distribution?

A

protein-binding capacity -> drug capacity -> constant free fraction

39
Q

what form of drug and protein is active and inactive?

A
40
Q

where can drugs accumulate in the body and act as a resevoir?

A

fat, tissues, bone

41
Q

what does storage depots of drugs do to the drug?

A

decrease plasma levels and prolong half-lives

42
Q

what are the sites of drug exclusion

A

CSF, ocular fluid, endolymph fluid, fetal fluid, pleural fluid

43
Q

Equation of apparent volume of distribution

A
44
Q
A
45
Q

Calculate Vd

A
46
Q

when do we see a large Vd?

A

drugs that distribute extensively or bind extensively

47
Q

when do we see a low Vd?

A

drug mostly present in the plasma

48
Q

what is the principal goal of biotransformation of drugs and xenobiotics (foreign compounds)?

A

promote elimination from the body

49
Q

what are the qualities of most pharmacologically active drugs?

A

lipid soluble, unionized or partially ionized, strongly bound to plasma proteins, not readily excreted by kidney, tend to remain in body for a long time unless liver metabolizes them and kidney excretes them

50
Q

Define phase 1 reaction

A

convert lipid soluble parent compounds to more polar metabolites (less lipid soluble)

51
Q

Are most phase 1 metabolites excreted?

A

yes only some undergo phase 2 rxns before excreted

52
Q

what are the two phase 1 reactions?

A

non-microsomal (non-inducible)
microsomal (inducible)

53
Q

How are non-microsomal phase 1 rxns metabolized

A

esterases and amidases, monoamine oxidases, alcohol and aldehyde dehydrogenases

54
Q

How are microsomal phase 1 rxns metabolized

A

P450

55
Q

what does phase 2 synthetic reactions result in?

A

larger molecular weight, increased polarity, mostly inactive

56
Q

what is the only microbial phase 2 rxn? Is this inducible or non-inducible?

A

Glucuronidation, inducible rxn

57
Q

List phase 2 rxns

A

glucuronidation, acetylation, glutathione conjugation, glycine conjugation, suldation, methylation, water conjugation

58
Q

which phase reaction introduces or unmasks certain functional groups?

A

Phase 1 - OH, SH, NH2, etc.

59
Q

what is enterohepatic circulation of drugs

A

increases 1/2 life of drug
conjugate from liver metabolism goes back into SI via bile -> colon/rectum, bacteria in gut combines conjugate to form drug and it goes back into liver

60
Q

what contributes to renal excretion of drugs and drug metabolites?

A

glomerular filtration, active tubular secretion or reabsorption, passive diffusion across tubular epithelium

61
Q

what is clearance?

A

measure of capacity of body to remove drug

62
Q

Systematic clearance equation

A
63
Q

rate of elimination equation

A
64
Q

what two variables does clearance relate?

A

rate of drug elimination to its plasma concentration

65
Q

what is the 1/2 life equation?

A
66
Q

what is the kinetics of first order elimination?

A

-exponential
-constant proportion of drug eliminated in a unit time

67
Q

what is the first order elimination equation?

A
68
Q

Define half life

A

time required to change amount of drug in body by 50%

69
Q

Define zero order elimination

A

constant amount is eliminated in a unit time

70
Q

which order of elimination is associated with amount?

A

zero order

71
Q

which order of elimination is associated with proportion?

A

first order

72
Q

how many 1/2 lives does it take to obtain a steady state plasma level

A

5

73
Q

when does the biologic effect happen?

A

After steady state

74
Q

what is the relationship of concentration of steady state to dose and clearance?

A

Css directly proportional to dose
Css indirectly proportional to clearance

75
Q

how long do you have to wait before determining plasma steady state levels of the drug in the body?

A

5 half lives

76
Q

how many half lives does it take to eliminate most of the drug?

A

5 half lives

77
Q

what will shortening the dosing interval do to the steady state concentration

A

raise it

78
Q

what will lengthening the dosing interval do to the steady state concentration?

A

gradual dec of plasma level and lower steady state

79
Q

Is the time to reach steady state levels related to the size of the dose?

A

no

80
Q

Define loading dose

A

dose used to reach immediate therapeutic conc.

81
Q

what is the loading dose equation

A

loading dose = Vd x TC
TC (target conc.) = Css

82
Q

what is the dosing rate and elimination rate equation?

A
83
Q

what is the maintenance dose equation?

A
84
Q

what are the P450 inducers?

A

rifampin, barbiturates, phenytoin, glucocorticoids, st johns wort

85
Q

what are the P450 inhibitors

A

CYP3A4 inhibitors
cimetidine, ketoconazole, diltiazem, erythromycin, verapamil, fluoxetine

Pharmacology (8 decks)

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