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ICPP > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

What is pharmokinetics?

A

Looks at what the body does to drugs

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2
Q

What are the 4 main processes involved in the processing of drugs by the body?

A

Absorption
Distribution
Metabolism
Elimination

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3
Q

Administration of drugs can be grouped into which 2 categories?

A

Enteral = entry into the body via GI tract

Parenteral = entry into the body by all other routes (not GI tract)

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4
Q

What are the 3 methods of administering drugs enterally?

A

Oral
Sublingual
Rectal

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5
Q

What are some parenteral methods of administering drugs?

A 
Subcutaneous
Intravenous
Intramuscular 
Inhalation 
Intranasal
Transdermal
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6
Q

How are most drugs usually administered? Where is most of the drug absorbed?

A

Orally

In the small intestine

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7
Q

What happens to drugs administered orally in the stomach?

A

There is little absorption here - mixes with chyme —> small intestine

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8
Q

By which methods are drugs absorbed at the molecular level? (3)

A

Passive diffusion
Facilitated diffusion
Secondary active transport

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9
Q

Which drugs are likely to be absorbed by passive diffusion?

A

Lipophilic steroids

Weak acids/bases can diffuse passively - effectively lipophilic

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10
Q

Which drugs are likely to be absorbed by facilitated diffusion?

A

Molecules with an ionic charge, using its electrochemical gradient

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11
Q

What are SLCs

A

Solute carriers used to absorb drugs by facilitated diffusion

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12
Q

What two types of SLC are there? What does each SLC transport?

A

OATs (weak acids)

OCTs (weak bases)

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13
Q

Where are SLCs highly expressed?

A

In the GI, hepatic and renal epithelia

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14
Q

Does secondary active transport use ATP?

A

No

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15
Q

How is secondary active transport driven?

A

By pre-existing electrochemical gradients

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16
Q

Give an example of a drug that is transported via secondary active transport?

A

Fluoxetine - cotransported with Na ions

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17
Q

What factors can affect drug absorption?

A 
Blood flow 
Surface Area/GI length
Lipophilicity of the drug
Density of SLC expression 
GI motility
Food/pH
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18
Q

How are drugs metabolised in the liver?

A

By cytochrome P450 (phase 1 enzyme) and conjugating (phase 2 enzyme)

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19
Q

What is first pass metabolism? What effect does this have on the [drug] reaching the systemic circulation?

A

Metabolism of drugs in the liver by phase 1 and phase 2 enzymes —> decreases [drug] reaching systemic circulation

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20
Q

What is bioavailability?

A

The fraction of a defined does that reaches its way into a specific body compartment

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21
Q

What is used as a reference when calculating the bioavailability of a drug?

A

IV used as a reference to compare to other routes

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22
Q

Bioavailability values are always…

A

Between 0 and 1 (decimal preferred)

23
Q

What is the importance of the bioavailability value, how is it used?

A

Used to inform choice of administration route

24
Q

How are drugs distributed in the body?

A

By bulk flow from arteries to capillaries

Then by diffusion from capillaries to interstitial fluid to cell membranes to targets

25
Q

What factors affect drug distribution in the body?

A

Drug lipophilicity/hydrophilicity
Capillary permeability
Drug pKa and local pH
Presence of OATs and OCTs

26
Q

What can drugs bind to which prevent them reaching their target sites?

A

Blood plasma proteins, such as albumin/globulins

27
Q

What is the nature of the bonding of drugs to plasma proteins?

A

Not strong, bound and unbound in equilibrium

28
Q

How many litres of water are there in the body of a typical adult?

A

42 litres

29
Q

How is the 42 litres of water found in a typical adult split into intracellular and extracellular?

A 
Intracellular = 28 litres (2/3)
Extracellular = 14 litres (1/3)
30
Q

How is the 14 litres of extracellular water found in a typical adult split?

A

3 litres in the plasma

11 litres interstitial

31
Q

What is Vd (volume of distribution) a measure of?

A

Summarises the movement of the drug through body compartments

32
Q

What does a small Vd value mean?

What does a large Vd value mean?

A

Low penetrance of the drug into interstitial and intracellular compartments

Greater penetrance of the drug into interstitial and intracellular compartments

33
Q

How does drug metabolism largely take place?

A

In the liver via phase 1 and phase 2 enzymes

34
Q

What do enzymes in the liver do to drugs to enhance renal elimination?

A

Increase their ionic charge

35
Q

What happens to lipophilic drugs during elimination?

A

They diffuse back into the plasma

36
Q

What typically happens to drugs after metabolism?

A

They are inactivated

37
Q

What is phase 1 metabolism carried out by? Where are the enzymes found?

A

Cytochrome P450 enzymes

On the ER

38
Q

What happens to drugs in metabolism?

A

They are given an increased ionic charge - through oxidation/reduction reactions (phase 1 metabolism) or through conjugating (phase 2)

39
Q

Give an example of a drug that is metabolised into its active form by phase 1 metabolism?

A

Codeine to morphine

40
Q

What is phase 2 metabolism carried out by?

A

Hepatic enzymes

41
Q

What is the function of phase 2 metabolism?

A

Enhances hydrophilicity by further increasing ionic charge

Enhances renal elimination

42
Q

What is CYP450 induction? How can this affect the effectiveness of the drug?

A

Where certain drugs induce specific CYP450 isoenzymes

Can result in decreased plasma levels of the drug and activity of certain drugs as they are being metabolised at a greater rate

43
Q

What is CYP450 inhibition? What affect can this have on the effectiveness of the drug?

A

Certain drugs can inhibit specific CYP450 isoenzymes

Results in increased plasma levels of the drug and increased activity as metabolism of drug is slowed

44
Q

Most drug elimination is carried out by the…

A

Kidney

45
Q

How are drugs eliminated in the kidneys?

A

Via active tubular secretion

There is a high expression of OATs and OCTs which carry ionised molecules into the proximal tubule for secretion

46
Q

What is clearance of a drug?

A

The RATE of elimination of a drug from the body

47
Q

Generally Total Body Clearance is equal to…

A

Hepatic clearance + Renal clearance

48
Q

What is clearance measured in?

A

Ml/min

49
Q

What 2 factors is drug half life dependent on?

A

Drug clearance

Volume of distribution of a drug

50
Q

What is drug half life?

A

The amount of time over which the [drug] in plasma reduces to half of its initial concentration when it was first measured

51
Q

Assuming there are plenty of OATs/OCTs and phase 1/2 enzymes, metabolism and excretion of a drug is said to be _________ to the [drug] and is described as showing __________ kinetics

A

Proportional

First order

52
Q

When does zero order kinetics for a drug occur?

A

When the elimination processes are saturated

At higher doses for most drugs - zero order kinetics will occur

53
Q

Drugs at or near the dose that gives zero order kinetics are more likely to result in….

A

Adverse drug reactions

Toxicity

54
Q

Eliminations are more likely to become saturated in what circumstances?

A

Reduced hepatic/renal capacity

ICPP (8 decks)

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