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Medicine Year 1 - Semester 2 - Part 2 > Pharmacokinetics 1 > Flashcards

Pharmacokinetics 1 Flashcards

1
Q

Pharmacokinetics

A

What the body does to the drug

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2
Q

State the 4 main processes of pharmacokinetics

A

(Liberation)

Absorption
Distribution
Metabolism
Excretion

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3
Q

Advantages of plasma used in transporting drugs

A

Easy convenient sampling pool, in which we can use to measure the amount of drug in the body

OR

A convenient way in which a drug is distributed in the body.

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4
Q

State some routes of drug administration

A

Oral
Sublingual
Inhalational
Topical
Transdermal
Intramuscular
Intravenous

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5
Q

Advantages and Disadvantages of the oral route

A

A: Convenient

D: First pass effect, many variables and barriers

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6
Q

Advantages and Disadvantages of the sublingual route

A

A: No first-pass effect

D: Inconvenient, small dose limit

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7
Q

Advantages and Disadvantages of the inhalational route

A

A: Fast, rapid delivery to blood

D: Requires special properties of drug (vaporised, atomised)

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8
Q

Advantages and Disadvantages of the topical route

A

A: Convenient, Localised

D: Only local

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9
Q

Advantages and Disadvantages of the transdermal route

A

A: Prolonged release

D: Skin very effective barrier

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10
Q

Advantages and Disadvantages of the intramuscular route

A

A: Rapid for aqueous, slow for oil

D: Painful, requires trained personnel

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11
Q

Advantages and Disadvantages of the intravenous route

A

A: Direct, total dose, rapid

D: Requires professional, infection risk, rapid response

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12
Q

First-pass effect

A

Any barrier between the drug being administered to your patient and it getting into the plasma.

Anything that metabolises/transforms/changes the drug due to the interaction of enzymes.

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13
Q

Bioavailability

A

The fraction of unchanged drug that reaches the systemic circulation.

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14
Q

Alun - bioavailability definition

A

How much of the administered dose you would expect to see get into the patients plasma.

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15
Q

IV injection bioavailability

A

100%

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16
Q

Bioavailability equation

A

(AUC oral / AUC IV) x 100%

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17
Q

State the 4 ways that small molecules can cross cell membranes

A
  1. Diffusing directly through the lipid
  2. Diffusing through aqueous pores
  3. Transmembrane carrier protein
  4. Pinocytosis
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18
Q

Feature of drug to : diffuse directly through the lipid

A

Drug should be:

  • Uncharged
  • Lipophilic enough
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19
Q

Feature of drug to : use a transmembrane carrier protein

A

Drug should be:

  • Charged
  • Hydrophilic
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20
Q

When is diffusion through aqueous pores used ?

A

More likely important for diffusion of gases.

Aqueous pores are VERY small.

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21
Q

When is pinocytosis used ?

A

Mostly macromolecules, not drugs.

(for larger molecules: proteins/peptides)

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22
Q

Describe hydrophilic drugs

A

Hydrophilic drugs are soluble in aqueous, polar media.

Cannot pass through the lipid bilayer

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23
Q

Describe lipophilic drugs

A

Lipophilic drugs are soluble in fats and non-polar solutions.

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24
Q

Describe polar media

A

Blood plasma
Cytosol
Interstitial fluid

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25
Q

Describe non-polar solutions

A

Interior of lipid bilayer and fat

26
Q

Feature of drugs

A

Many drugs are weak acids or bases

  • ionised:unionised ratio depends on pH
  • ionised drugs have low lipid solubility
27
Q

Gastric Acid pH

A

1-3

28
Q

Large Intestine pH

A

8

29
Q

Small intestine pH

A

5-6

30
Q

Plasma pH

A

7.4

31
Q

What drug properties affect absorption ?

A

Lipophilicity
Ionisation

32
Q

When do barriers to absorption arise ?

A

Unless the drug is directly injected into systemic circulation.

33
Q

Factors that affect distribution

A

Degree of drug ionisation
Lipid solubility
pH of compartments

Cardiac output and blood flow
Capillary permeability

Plasma protein binding

34
Q

Compartment model - state some places drugs may go to

A

(from shortest to longest time)
Vessel Rich Group (VRG) - kidneys
Muscle
Adipose

35
Q

Key feature of compartment model

A

Not all drugs will distribute evenly around the body

Some will go and accumulate in different locations.

The further away the drug gets from plasma and the more likely it is to accumulate in distant tissues, the harder it is to get rid of that drug from the body.

This is because the route out of the drug from the body is also via the plasma.

36
Q

What are Bisphosphonates ?

A

Treatment given to reduce the burden of osteoporosis.

Work by killing off osteoclasts, (bone resorbing cells which degrade and remove bone from the body)

37
Q

Mechanism of action of bisphosphonates

A

Phosphate groups have a high affinity for calcium, so the bisphosphonates will bind VERY strongly to bone where there is a high degree of calcium.

38
Q

Key feature of bisphosphonates

A

Quickly distributed to the skeleton

Long time to remove drug as it binds so strongly to bone.

39
Q

State the 2 types of bisphosphonate

A

Oral alendronate
IV zoledronate

40
Q

Oral alendronate

A

Daily/weekly

41
Q

IV zolendronate

A

Yearly

42
Q

Why is zolendronate given by IV only ?

A

Any dietary source of calcium will be bound to by this.

It would bind to calcium in the GI tract and not get absorbed.

43
Q

Protein binding

A

A drug must be free to distribute widely or bind to its receptor

44
Q

State some drugs that bind to plasma proteins

A

Albumin
alpha-1 acid glycoprotein

Lipoproteins
Globulins

45
Q

Albumin

A

A lot of drugs that will stay in high concentrations in the plasma will bind to albumin and stay there.

46
Q

Importance of drugs binding to albumin

A

ONLY drugs which are unbound can interact with receptors / get from the plasma into other tissues.

So those bound to albumin cannot interact.

47
Q

% unbound drugs

A

Fraction of unbound drugs can be as low as 1%

48
Q

What does competition for binding sites cause ?

A

Can cause big increases in free drug concentrations.

49
Q

Feature of warfarin and aspirin

A

98% of warfarin bound to albumin.
Aspirin has a high affinity for albumin…

So in the presence of aspirin competition occurs and whichever has the highest affinity for the site is likely to win.

50
Q

Which has a higher affinity for albumin, aspirin or warfarin ?

A

Aspirin

51
Q

Increased Aspirin levels results in:

A

Increased warfarin available in the plasma

52
Q

Describe distribution between body fluid compartments

A

Permeability across tissue barriers

Binding within compartments

pH partition

Fat:Water partition

53
Q

What does degree of distribution between compartments depend on ?

A

Tissue and Drug dependent factors

54
Q

Where is body water distributed ?

A

Distributed into 4 main compartments

55
Q

How can side-effects of some drugs be minimised ?

A

By limiting their distribution via the route of administration.

56
Q

Muscarinic Ach receptor agonists

A

Pilocarpine
Bethanechol

57
Q

Pilocarpine

A

Non-selective muscarinic agonist

Constricts pupils
Glaucoma - decrease IOP
Xerostomia - following head/neck radiotherapy

58
Q

Bethanecol

A

Non-selective muscarinic agonist

Bladder and GI hypotonia

59
Q

Structure of bethanechol

A

Quaternary ammonium
POLAR substance
not readily absorbed

60
Q

Structure of pilocarpine

A

Tertiary amine

Medicine Year 1 - Semester 2 - Part 2 (53 decks)

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