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PharmSci ADME > Absorption > Flashcards

Absorption Flashcards

1
Q

How do drugs avoid 1st pass metabolism?

A

bypass the portal vein and enter systemic circulation

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2
Q

Which enteral routes of admin avoid 1st pass?

A
  1. Buccal/sublingual

2. Rectal

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3
Q

T/F Parenteral routes bypass 1st pass

A

False

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4
Q

T/F intranasal routes bypass 1st pass

A

true

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5
Q

T/F topical routes bypass 1st pass

A

true

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6
Q

T/F inhalation routes bypass 1st pass

A

false

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7
Q

The upper rectum bypass 1st pass

A

False, upper rectum vasculature is connected to portal vein so drugs are susceptible to 1st pass

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8
Q

For most drugs, the optimum site for drug absorption after oral administration is the ________

A

upper portion of SI or duodenum region

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9
Q

What is unique about the duodenum that allows the drug to diffuse passively?

A

immense SA

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10
Q

The duodenal region is highly perfused with a network of capillaries which helps maintain a _________ from the intestinal lumen and plasma circulation

A

concentration gradient

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11
Q

Where is the most rapid drug absorption?

A

Duodenal area of SI

- due to villi and microvilli

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12
Q

Why does the colon have limited drug absorption?

A
  • lack of villi
  • lack of SA
  • lack of blood flow
  • more viscous and semisolid nature of lumen contents
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13
Q

Ethanol absorption

A
  • completely miscible with water
  • easily crosses cell membranes
  • efficiently absorbed from stomach
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14
Q

What kind of drugs can be absorbed from the stomach through passive diffusion?

A

fat soluble, acid stable

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15
Q

_________ exists for efficient absorption and drugs should be released from dosage form completely during this

A

anatomic absorption window

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16
Q

What is gastric emptying delayed by?

A

high fat meals
cold beverages
anticholinergic drugs

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17
Q

What does a delay in gastric emptying cause?

A

slow rate of drug absorption because it delays drug reaching duodenum

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18
Q

What kind of drugs degrade if gastric emptying is delayed?

A

unstable drugs (penicillin)

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19
Q

Are liquids or solids digested faster from the stomach?

A

liquids and small particles

- emptied due to higher basal pressure in stomach over duodenum

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20
Q

Large particles are delayed for ______ by the presence of food in stomach

A

3-6 hours

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21
Q

Indigestible solids

A
  • empty slowly
  • mainly during inter digestive phase when food is not present and stomach is less motile
  • periodically empties due to housekeeper wave contraction
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22
Q

Gamma scintigraphy

A
  • label drug dosage with y-emitting radio nucleotide that is NOT absorbed by patient and can be excreted
  • Correlates residence time of drug in a given region after the dosage form is broken up to absorption
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23
Q

______ added to dosage form reduces uptake of drugs absorbed exclusively from SI

A

mannitol

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24
Q

____ slows GI transit, decreases stool water content and decreases drug absorption

A

Codeine

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25
Q

______ accelerates GI transit, increases stool water content and increases drug absorption

A

Lactulose

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26
Q

GI perfusion

A
  • study absorption and permeability of drug in various segments of GI tract
  • jejunum typical choice because of lower peristaltic activity than duodenum
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27
Q

What is caco-2 cultures used for?

A
  • study permeability of passively transported drugs

- classify BCS classes of drugs

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28
Q

Class I of BCS

A
  • drug dissolves rapidly
  • well absorbed
  • high solubility
  • higher permeability
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29
Q

Class II of BCS

A
  • drug is dissolution limited
  • well absorbed
  • low solubility
  • high permeability
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30
Q

Class I bioavailability

A

problem not expected for IR drug products (APAP)

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31
Q

Class II bioavailability

A

controlled by dosage form and rate of release of drug substance (Ibuprofen, Naproxen)

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32
Q

Class III of BCS

A
  • permeability limited

- high solubility

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33
Q

Class III bioavailability

A
  • may be incomplete if drug is not released and dissolved within absorption window (Atenolol, penicillins)
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34
Q

Class IV of BCS

A
  • low solubility

- low permeability

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35
Q

Class IV bioavailability

A
  • difficult in formulating a drug product that will deliver consistent drug bioavailability
  • alternate route of admin may be needed (Amphotericin B, Neomycin)
36
Q

Lipinskis RO5

A
  • MW <500
  • H Bond donors <5
  • H bond acceptors <10
  • LogP <5
37
Q

What is the 1st barrier to gastric emptying?

A

pyloric sphincter muscle

38
Q

How does the presence of food affect drug absorption?

A
  • may delay gastric emptying
  • increase blood flow
  • changes in pH
  • food may interact with drug
  • bile flow stimulated
  • change in metabolism/excretion within GI tract
39
Q

Water and drug absorption

A
  • larger volumes of water increase solubility of drug
40
Q

T/F disintegrating tablet absorption is delayed by presence of food

A

False

- smaller particles absorbed more consistently regardless of food presence

41
Q

What is the double-peak phenomenon in drug PK profiles?

A

delayed gastric emptying due to presence of food can result in lower dissolution –> double peak in Cmax

42
Q

What molecules can pass through cell membranes?

A

water, selected small molecules, lipid-soluble

43
Q

What molecules cannot pass through cell membranes?

A

highly charged, large

44
Q

In a cell membrane how can polar molecules and charged ions cross?

A
  • globular proteins embedded in matrix
45
Q

Transcellular transport

A
  • determined by ease of drug permeability across lipid molecules
46
Q

Is transcellular or paracellular transport best for small lipophilic drugs?

A

transcellular

47
Q

Paracellular transport

A
  • through water filled junctions between cells
48
Q

T/f active and passive transport are saturable processes

A

False

- only AT because there is only so many transporters availabilt

49
Q

Flux units

A

mass/unit area (mg/cm2)

50
Q

Flux

A

rate of transfer

51
Q

Ficks law of diffusion

A

molecules diffuse from a region of high concentration to a region of low concentration (Flux)

52
Q

Ficks law equation

A

dQ/dt = (DAK/h)(Cgi-Cp)

dQ/dt = P(Cgi)

53
Q

K in fick’s law

A
  • higher K favors absorption

- more lipid soluble have larger K

54
Q

A in ficks law

A
  • higher A favors absorption
55
Q

What order process is extravascular absorption usually?

A

1st order

56
Q

Passive transport

A
  • ionization of weak electrolytes

- unequal concentration of ionizable drugs on either side of membrane if pH is different

57
Q

pH partition hypothesis (if pH on one side of a barrier differs)

A
  • drugs will ionize to different degrees on either side
  • total drug concentrations on two sides will be unequal
  • the side where the drug is more ionized will contain greater portion of drug
58
Q

Weak acid/weak base absorption

A
  • WA (salicylic acid): rapidly absorbed from stomach

- WB (ephedrine): poorly absorbed from stomach

59
Q

How can drugs be absorbed through carrier-mediated transport?

A

drugs structurally resemble natural substrates in body to allow for carriers to recognize them for transport

60
Q

Active transport at higher concentrations, the rate of drug absorption remains ______

A

constant, zero order

61
Q

What is the function of efflux drug transporters?

A

protect body from undesirable compounds by pumping drugs out of body (pgp, MDR)

62
Q

______ are intestinal epithelial absorptive cells the express transporters

A

enterocytes

63
Q

What is multi drug resistance in cancers caused by?

A

efflux transporter proteins such as pgp

64
Q

How do disintegrates affect absorption?

a. Ka (absorption rate constant)
b. tmax
c. AUC

A

a. promote disintegration = more SA for absorption
b. decreases (faster)
c. increase due to more drug into circulation (better bioavailability)

65
Q

How do lubricants affect absorption?

a. Ka (absorption rate constant)
b. tmax
c. AUC

A

a. decrease absorption by decreasing disintegration due to more lipophilic
b. increases
c. decreases due to slower rate

66
Q

How do coating agents affect absorption?

a. Ka (absorption rate constant)
b. tmax
c. AUC

A

NO effect

67
Q

How does enteric coating affect absorption?

a. Ka (absorption rate constant)
b. tmax
c. AUC

A

a. decrease (delayed disintegration)
b. increases
c. decreases due to slower rate

68
Q

How do sustained release agents affect absorption?

a. Ka (absorption rate constant)
b. tmax
c. AUC

A

a. decrease (delayed disintegration)
b. increases
c. decreases due to slower rate

69
Q

When is food effect most pronounced on absorption?

A

when drug is taken shortly after meal

70
Q

What is most likely to affect GI physiology and absorption?

A

high calorie

high fat

71
Q

What can you use to study the effect of food on bioavailability?

A

high calorie and high fat meals

72
Q

Food increases absorption of __ drugs

A

lipid soluble

73
Q

Food stimulates production of _____, which increases solubility of fat-soluble drugs

A

bile acids

74
Q

Basic drugs and absorption

A
  • benefit from presence of food in stomach because it stimulates HCL acid secretion
  • lowers pH
  • more rapid dissolution of drug and better absorption
75
Q

Grapefruit juice and absorption

A
  • inhibits CYPS (involved in drug metabolism)

- increases absorption of a drug

76
Q

Pregnancy and absorption

A
  • delayed gastric emptying and SI motility result in
    1. increase Tmax
    2. decreased Cmax
    3. AUC decreased
77
Q

CHF and absorption

A
  • decreased rate of drug removal from SI = lower bioavailability due to concentration gradient altered
  • increased tmax
  • decreased cmax
  • decreased rate = lower AUC
78
Q

Achlorhydria and absorption

A
  • acid production = low
  • decreased absorption of weak base drugs
  • co admin of acidic beverages can enhance absorption
79
Q

Crohn’s disease and absorption

A
  • decreased SI transit time
  • lower SA available due to inflammation
  • erratic and unpredictable effects on absorption
80
Q

PPI and absorption

A
  • decrease gastric acid production
  • increase gastric pH
  • may interfere with BA of drugs with gastric absorption
81
Q

What may cause premature drug release from enteric coated tablets due to early dissolution at higher pH (dose dumping)

A

PPIs

82
Q

Celiac disease and absorption

A
  • increased gastric emptying
  • increased permeability of SI
  • unpredictable effects
83
Q

cholesyramine effects on absorption

A

binds to drugs to remove them from the body

84
Q

Drugs with decreased bioavailability with food

A
  • doxycycline
  • atorvastatin
  • plavix
  • alendronate
  • flomax
85
Q

drugs with increased bioavailability with food

A
  • oxycodone
  • metaxalone
  • spironolactone
86
Q

What is the rate limiting step of drug dissolution?

A

solubility

PharmSci ADME (4 decks)

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