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Principles of Disease > Drug Absorption > Flashcards

Drug Absorption Flashcards

1
Q

What is the pharmaceutical process

A

Getting the drug into the patient

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2
Q

What is the pharmacokinetic process

A

Getting the drug to the site of action

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3
Q

What is the pharmacodynamic process

A

Producing the correct pharmacological effect

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4
Q

What is the therapeutic process

A

Producing the correct therapeutic effect

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5
Q

What factors determine drug pharmacokinetics

A 
Absorption
Distribution
Metabolism
Elimination
(ADME)
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6
Q

What do the factors of pharmaknetics enable us to understand

A 
Dosage 
Drug administration
Drug handling 
Patient variability
Potential for harm
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7
Q

What is absorption in relation to pharmakinetics

A

The process of movement of unchanged drug from the site of administration to the systemic circulation

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8
Q

How can drugs be absorbed into the system

A 
Oral
Intravenous
Subcutaneous 
Intramuscular
Other GI - Sublingual, rectal
Inhalation
Nasal
Transdermal
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9
Q

What enables most drugs to have biological action

A

Drugs must enter the blood stream and be distributed to a site of action

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10
Q

There is always a correlation between plasma concentration of a drug and what

A

The therapeutic response

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11
Q

What is Tmax

A

Time to peak concentration

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12
Q

What is Cmax

A

The peak concentration

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13
Q

What is AUC

A

Area under the drug concentration-time curve which represents the amount of drug which reaches the systemic circulation

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14
Q

If the rate of absorption is rapid what happens to the drug concentration peak

A

It will be earlier (Tmax)

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15
Q

If the drug dose is increases what happens

A

Time to peak concentration will not be affected (Tmax)

Peak concentration will increase (Cmax)

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16
Q

What is a therapeutic range

A

A drug is active over a range of concentrations

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17
Q

What happens below and above the therapeutic range

A

Below: insufficient or no pharmacological action
Above: toxicity

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18
Q

What is a therapeutic index

A

A measure of the range at which a drug is safe and active

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19
Q

What is bioavailability

A

The amount of drug which reaches circulation and which is available for action

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20
Q

How can bioavailability be estimated

A

Using AUC

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21
Q

How much bioavailability does a drug given intravenously have

A

100%

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22
Q

State the factors which can affect bioavailability

A

Formulation
Ability of drug to pass physiological barriers
Gastrointestinal effects
First pass metabolism

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23
Q

How does formulation affect bioavailability

A

Due to the slow release preparations

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24
Q

What physiological barriers are there that can affect bioavailability

A

It is dependent on:
Particle size
Lipid solubility
pH and ionisation

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25
Q

What gastrointestinal effects affect bioavailability

A

It is dependent on:
Gut motility
Food
Illness

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26
Q

What does the degree of ionisation of drugs depend on

A

Most drugs are weak acids or bases so they depend on the pH of the environment

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27
Q

What forms of the drug will be present in solution

A

Ionised and un-ionised forms

28
Q

What can the ionised form of the drug not cross

A

Membrane

29
Q

What will the un-ionised form of the drug do

A

Distribute across the membrane until equilibrium is reached

30
Q

What is ion trapping

A

An acidic drug being more concentrated in the compartment with high pH

31
Q

**What equation describes the relationship between the local pH and the degree of ionisation

A

Henderson-Hasselbalch equation

32
Q

How can a small change in pH affect the drug

A

May significantly influence the ionisation of a drug, so the rate of absorption or diffusion.

33
Q

What is required for a drug to be able to pass a lipid layer

A

Must be in solution and be lipid soluble

34
Q

What is a lipid-water partition coefficient

A

The ability of a drug to diffuse across a lipid barrier

It is the ratio of the amount of drug which dissolves in the lipid and water phase when they are in contact

35
Q

What will happen to a highly lipid soluble drug

A

It will rapidly diffuse across a cell membrane to reach the brain, ovaries, testes and liver

36
Q

What will happen to a non lipid soluble drug

A

May not be absorbed at all e.g. gentamicin

37
Q

Describe the features of passive diffusion

A 
Occurs along concentration gradient. 
Non selective 
Not saturable 
Requires no energy 
No carrier is needed 
Depends on lipid solubility and degree of ionsation
38
Q

How common is passive diffusion

A

Its very common

39
Q

How is common is active diffusion

A

Relatively unusual

40
Q

Describe the features of active absorption

A 
Occurs against concentration gradient 
Requires carrier and energy
Specific 
Saturable
Iron ,K , Na , Ca 
Uptake of levodopa by brain
41
Q

What is active absorption

A

Energy dependent transport across membranes against a concentration gradient

42
Q

What features must drugs have to undergo active absorption (transport)

A

Resemble naturally occurring compounds

Drug must be reversibly bound to a carrier system

43
Q

Describe the features of facilitated diffusion

A 
Occurs along the concentration gradient
Require carriers
Saturable 
Structure specific
No energy required
Mixed order kinetics
44
Q

Where does filtration normally occur

A

Through channels in the cell membrane

45
Q

What should the molecular weight of drugs be to undergo filtration

A

Low molecular size (smaller than the diameter of the pore)

Mmolecular weight of 100 or less

46
Q

What is the driving force for the passage of drugs in filtration

A

Hydrostatic or the osmotic pressure difference across the membrane

47
Q

What type of drugs normally undergo filtration

A

Water-soluble drugs e.g. urea, water & sugars, renal excretion, removal of drug from CSF & entry of drug into the liver

48
Q

How can motility affect drug absorption

A

Speed of gastric absorption will affect speed at which drug reaches site of absorption
Can be affected by other drugs, food/drink and illnesses

49
Q

Where are most drugs absorped

A

Small intestine

50
Q

How can food affect drug absorption

A

Can enhance or impair rate of absorption

51
Q

How can illness affect drug absorption

A

Malabsorption (e.g. Coeliac disease) can increase or decrease rate of absorption
Migraine reduces rate of stomach emptying and therefore rate of absorption of analgesic drugs

52
Q

How are most drugs given

A

Orally

53
Q

What is first pass metabolism

A

Metabolism of drug prior to reaching systemic circulation

54
Q

Where can first pass metabolism occur

A 
Gut lumen (acid, enzymes)
Gut wall (metabolic enzymes)
Liver (hepatic enzymes)
55
Q

Which factors should be considered when administering drugs using subcutaneous/intramuscular methods

A

The rate of absorption from these sites change with different physical properties of formulation
Depends on blood flow to site
Needs small volume
Avoids first pass metabolism
Some drugs not well absorbed from this route

56
Q

What is sublingual absorption

A

Under the tounge

57
Q

How does sublingual absorption work

A

Sublingual absorption from the buccal mucosa bypasses first pass metabolism which will inactivate the drug
The drugs given this way enter the circulation directly e.g. GTN for angina

58
Q

Describe rectal administration

A

Drugs given via the rectum bypass first pass metabolism

Absorption tends to be slow

59
Q

Why are some drugs administered through the rectum

A

Rectum is often used for drugs which cause irritation of the stomach

60
Q

What is inhalation/nasal administration dependent on

A

Type of delivery system, particle size, patient technique

61
Q

What are the advantages of inhalation/nasal administration

A

Better for volatile agents
Can be metabolism in lungs
Relatively rapid action

62
Q

What are the disadvantages of inhalation/nasal administration

A

About 5-10% absorbed

63
Q

When is inhalation/nasal administration normally used

A

For topical effect

To avoid problems of oral absorption (e.g. nausea)

64
Q

Describe transdermal administration

A

Avoids first pass metabolism
Can provide controlled release
Few substances well absorbed
Need to be non-irritant

65
Q

What needs to be considered when deciding for the mode of administration

A 
Purpose and site of drug action (local absorption, avoid first pass metabolism)
Disease effects
Patients ability to take medicine
Speed of action
Reliability of absorption

Principles of Disease (41 decks)

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