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Y2S2 GI > Drug Absorption > Flashcards

Drug Absorption Flashcards

1
Q

Bioavailability

A

Fraction of unchanged drug that reaches the systemic circulation
IV injection gives 100% bioavailability

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2
Q

Bioequivalence

A

Generics vs therapeutic substitutions

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3
Q

Generics must have a bioavailability of

A

80-125% compared to the reference product (EU reg.)

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4
Q

Generic substitution

A

when a different formulation of the same drug is substituted

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5
Q

Therapeutic substitution

A

the replacement of the originally-prescribed drug with an alternative molecule with assumed equivalent therapeutic effect. The alternative drug may be within the same class or from another class with assumed therapeutic equivalence.”

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6
Q

Advantages of oral route

A

– Cheap
– Safe
– Convenient

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7
Q

disadvantages of oral route

A

– Patient compliance

– Variation in bioavailability of drug

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8
Q

Journey of an oral drug

A 
oral dose
destroyed in gut 
not absorbed 
destroyed by gut wall 
destroyed by liver
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9
Q

Buccal / sublingual mucosa

A

– Direct absorption in to bloodstream
– Avoids first pass metabolism
– Not ideal surface for absorption

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10
Q

Gastric mucosa

A

– Enteric coating

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11
Q

Small intestine

A

– Main site of drug absorption

– Large surface area, more neutral pH

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12
Q

Large intestine / colon

A

– Poor absorption, long transit times

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13
Q

rectal mucosa

A
  • direct to systemic circulation
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14
Q

Four ways small molecules cross cell membranes

A
  1. diffusing directly though the lipid
    - lipid solubility is important
  2. diffusing through aqueous pores
    - more likely for diffusion of gases
  3. transmembrane carrier protein
    - solute carriers
  4. pinocytosis
    - mostly macromolecules
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15
Q

Weak bases

A

– Ionised in acidic pH

– Absorbed in small intestine – Ionisation in plasma?

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16
Q

Weak acids

A

– Unionised in acidic pH
– BUT also absorbed in small
intestine
• Large surface area

17
Q

what is the general rule when it comes to food and drug absorption

A

slows down the rate of gastric emptying

18
Q

why would food cause decreased absorption

A

intestinal motility

interactions with food, acids and presystemic metabolism

19
Q

why would food delay absorption

A

gastric emptying, Cmax may be decreased (maximum concentration that a drug achieves in tested area after the drug has been administrated)

20
Q

why would food cause increased absorption

A

poorly water soluble drugs

  • increased solubilisation
  • decreased presystemic metabolism
21
Q

what things should you consider when thinking about the interaction between drugs and food

A

is the drug an irritant?

  • solid vs liquid
  • protein and fat content
  • other dietary factors
22
Q

Levodopa uptake

A
  • Prodrug, treatment of Parkinson’s disease
  • Rapidly taken up from stomach and small intestine by LNAA transport carrier
  • HOWEVER DOPA decarboxylase is present in the gastric mucosa and this causes the DOPA > dopamine reaction and then dopamine is hydrolysed and doesn’t last long so this medication is normally taken with something which inhibits this enzyme
23
Q

Altered rate of drug absorption due to disease state

A 
increased = crohns 
decreased = coeliac disease
24
Q

factors that affect oral absorption

A

Particle size and formulation
GI motility
First pass metabolism
– First pass metabolism by gut wall or hepatic enzymes Physicochemical factors
– Direct drug interactions, dietary factors, varying pH

25
Q

Subcutaneous

A

– Slow absorption due to blood flow

26
Q

Intramuscular

A

– Lipophilic drugs rapidly
– Polar drugs via bulk flow and endothelial cell junctions
– High MWT or very lipophobic drugs via lymphatics

27
Q

Rate of onset

A

– Extent of capillary perfusion
– Drug vehicle
– Affected by factors that alter perfusion

28
Q

Inhalation

A 
Alveolar epithelium and bronchial mucosa
Systemic effects
• Lipid-solubledrugs
– Volatile / gaseous anaesthetics
• Drugs of abuse
• Accidental poisoning
29
Q

inhalation local effects

A

– Modify structure (ipratropium)
– Particulate size (salbutamol)
– Selectivity for receptors (salbutamol)
– Rapid breakdown in circulation (fluticasone)

30
Q

Intranasal advantages

A

Easily accessible, rich vascular plexus
• Avoids hepatic first pass metabolism
• Ease ,convenience, safety

31
Q

Intranasal limitations

A

• Limited drugs suitable

– Requires concentrated drug

32
Q

Topical route

Healthy skin is a barrier

A

– Stratified, squamous epithelium
– Keratinised layer
– Sebaceous gland secretions

33
Q

local effects of topical route

A

– Corticosteroids for eczema (hydrocortisone)
– Antihistamines for insect bites (mepyramine)
– Local anaesthetics (EMLA)

34
Q

systemic effects of topical route

A

– Transdermal patches (HRT, GTN, nicotine)

– Accidental poisoning (AChEsterase insecticides)

Y2S2 GI (26 decks)

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