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MD3002 Pharmacology > Drug Absorption > Flashcards

Drug Absorption Flashcards

1
Q

What is the bioavailability of IV injection?

A

100%

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2
Q

What is bioavailability?

A

Fraction of unchanged drug that reaches the systemic circulation

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3
Q

What does the area under a palsma concentration against time curve represent?

A

The overall exposure to the patient

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4
Q

What must generics’ bioavailibility be in comparison with the reference product *EU reg.)?

A

80 - 125%

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5
Q

What is a generic subsitution?

A

Occurs when a different formulation of the same drug is substituted

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6
Q

What is 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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7
Q

What class of drug can have its affects greatly altered by generic substitution?

A

Antipsychotics

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8
Q

What are the advantages of the oral route?

A
  • Cheap
  • Safe
  • Convenient
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9
Q

What are the disadvantages of the oral route?

A
  • Patient compliance

- Variation in bioavailability of drug

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10
Q

What factors can cause an oral drug to not reach systemic circulation?

A
  • Destroyed in gut
  • Not absorbed
  • Destroyed by gut wall
  • Destroyed by liver
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11
Q

Describe the features of the buccal / sublingual mucosa?

A
  • Direct absorption into blood stream
  • Avoids first pass metabolism
  • Not ideal surface for absorption
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12
Q

Where is the main site of drug absorption?

A

SI

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13
Q

What is the advantage of absorption via the rectal mucosa?

A

Direct to systemic circulation

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14
Q

What are the 4 ways small molecules cross cell membranes?

A
  • Diffusing directly through lipid
  • Diffusing across aqueous pores (more likely important for diffusion of gases)
  • Transmembrane carrier protein (e.g solute carriers)
  • Pinocytosis (mostly macromolecules, not drugs)
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15
Q

What are the feautures of weak bases?

A
  • Ionised in acidic pH
  • Absorbed in SI
  • Ionisation in plasma?
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16
Q

WHat are the features of weak acids?

A
  • Unionised in acidic pH
  • BUT also absorbed in SI
    Large surface area
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17
Q

What is the HEnderson-Hasselbach equation?

A

pKa - pH = log10([BH+]/[B])

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18
Q

What is the difference between the HH eqn when using a weak acid vs a weak base?

A
  • Acid = ionised form goes on bottom of eqn
  • Base = ionised form goes on top
  • H always stays on top
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19
Q

Will a weak acid more likely be more ionised or unionised form in the SI?

A

Unionised form - more likely to cross across the membrane into blood, more likely to become ionised in blood due to high pH which traps it in the blood

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20
Q

In general how does food affect gastric emptying?

A

Tends to slow the rate of gastric emptying

21
Q

What can happen as a result of food being prsesent in the GI tract?

A
  • Decreased absorption
  • Delayed absorption
  • Increased absorption
22
Q

What drugs can have an increased absorption as a result of food?

A

Poorly water soluble drugs

  • Increased solubilisation
  • Decreased presystemic metab
  • e.g propranolol
23
Q

What additional considerations should you think of in relation to the affects of food on drug absorption?

A 
Type of meal 
- Solid v liquid 
- Protein and fat content 
- Other dietary factors
Is the drug a GI irritant?
24
Q

What is the problem with taking levadopa and how is this problem fixed ?

A

Metabolised in GI (SI lumen) converted into dopamine which is very rapidly degraded and excreted (low bioavailability)

  • Carbadopa inhibits DOPA decarboxylase (inhibits presystemic metabolism of levadopa) which then allows for more levadopa to be absorbed and finally into dopanergic neurons
  • Increases pharmacological benefit
25
Q

What effect do antacids and ppis have which can affect drug uptake?

A

Change in gastric or intestinal pH

26
Q

What affect can laxatives and anticholenergics have which can affect drug uptake?

A

Change GI motility

27
Q

What affect can vasodilators have which can affect drug uptake?

A

Changes in GI perfusion

28
Q

What affect can neomycin have which can affect drug uptake?

A

Interferences with mucosal function (blunting ends of villi)

29
Q

What affect can tetracycline, calcium, magnesium have which can affect drug uptake?

A

Chelation (can bind to other drugs e.g biphsophonates and calcium)

30
Q

What affect can cholestryamine have which can affect drug uptake?

A

Resin binding

31
Q

What affect can charcoal have on drug uptake?

A

Adsorption

32
Q

How can coeliac disease affect drug absorption?

A

Blunting of villi less surface for uptake reduced uptake of drug

33
Q

How can ulcerative colitis affect drug absorption?

A

Can increase absorption

34
Q

What factors can affect oral absorption?

A
  • Particle size and formation
  • GI motility
  • First pass metabolism
  • Physicochemical factors
  • Splanchnic blood flow
  • Efflux pumps (P-glycoprotein)
35
Q

What are parenteral routes?

A
  • Subcutaneous

- Intramuscular

36
Q

What is absorption like for drugs administered via the subcutaneous route?

A

Slow due to poor blood flow

37
Q

What drugs are absorbed rapidly via IM route?

A
  • Lipophilic drugs rapidly
  • Polar drugs via bulk flow and endothelial cell junctions
  • High MWT or very lipophobic drugs via lymphatics
38
Q

What affects rate of onset of the parenteral route?

A
  • Extent of capillary perfusion
  • Drug vehicle
  • Affected by factors that alter perfusion
39
Q

What barriers do drugs which are inhaled bypass?

A

Alveolar epithelium and bronchial mucosa

40
Q

What do you need to take into account when prescribing inhaled medication?

A

Whether you want the effects of the drug on just the lungs or if you want them to reach the systemic circulation

41
Q

What drugs do you want to just have an effect on the lungs and not enter the systemic circulation?

A
  • Ipratropium
  • Salbutamol
  • Fluticasone
42
Q

What are the ways in which drugs will have a local affect and not affect systemic circulation?

A
  • Modified structure (become ionised)
  • Particle size
  • Selectivity for lung receptors
  • Once in the systemic circulation rapidly broken down
43
Q

What types of drugs do usually have a systemic affect but are inhaled?

A
  • Lipid soluble drugs
    Volatile / gaseous anaesthetics
  • Drugs of abuse
  • Accidental poisoning
44
Q

What are the advantages of the intranasal route?

A
  • Avoids hepatic first pass metabolism

- Ease, convenience, safety

45
Q

What are the limitations of the intranasal route?

A
  • Limited drugs available

- Requires concentrated drug

46
Q

What barriers are present in healthy skin?

A
  • Stratified, squamous epithelium
  • Keratinised layer
  • Sebaceous gland secretions
47
Q

Give some examples of some medications which are given topically

A
  • Corticosteroids for eczema (hydrocortisone)
  • Antihistamines for insect bites (mepyramine)
  • Local anaesthetics (EMLA)
48
Q

What are some of the ways / some examples of topical medications which can have a systemic effect?

A
  • Transdermal patches (HRT, GTN, nicotine)

- Accidental poisoning (AChEsterase insecticides)

49
Q

What must you remeber when applying topical medication which is likely to have a systemic effect?

A

SA to Volume ratio

MD3002 Pharmacology (7 decks)

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