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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
What gastrointestinal effects affect bioavailability
It is dependent on: Gut motility Food Illness
26
What does the degree of ionisation of drugs depend on
Most drugs are weak acids or bases so they depend on the pH of the environment
27
What forms of the drug will be present in solution
Ionised and un-ionised forms
28
What can the ionised form of the drug not cross
Membrane
29
What will the un-ionised form of the drug do
Distribute across the membrane until equilibrium is reached
30
What is ion trapping
An acidic drug being more concentrated in the compartment with high pH
31
**What equation describes the relationship between the local pH and the degree of ionisation
Henderson-Hasselbalch equation
32
How can a small change in pH affect the drug
May significantly influence the ionisation of a drug, so the rate of absorption or diffusion.
33
What is required for a drug to be able to pass a lipid layer
Must be in solution and be lipid soluble
34
What is a lipid-water partition coefficient
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
What will happen to a highly lipid soluble drug
It will rapidly diffuse across a cell membrane to reach the brain, ovaries, testes and liver
36
What will happen to a non lipid soluble drug
May not be absorbed at all e.g. gentamicin
37
Describe the features of passive diffusion
``` Occurs along concentration gradient. Non selective Not saturable Requires no energy No carrier is needed Depends on lipid solubility and degree of ionsation ```
38
How common is passive diffusion
Its very common
39
How is common is active diffusion
Relatively unusual
40
Describe the features of active absorption
``` Occurs against concentration gradient Requires carrier and energy Specific Saturable Iron ,K , Na , Ca Uptake of levodopa by brain ```
41
What is active absorption
Energy dependent transport across membranes against a concentration gradient
42
What features must drugs have to undergo active absorption (transport)
Resemble naturally occurring compounds | Drug must be reversibly bound to a carrier system
43
Describe the features of facilitated diffusion
``` Occurs along the concentration gradient Require carriers Saturable Structure specific No energy required Mixed order kinetics ```
44
Where does filtration normally occur
Through channels in the cell membrane
45
What should the molecular weight of drugs be to undergo filtration
Low molecular size (smaller than the diameter of the pore) | Mmolecular weight of 100 or less
46
What is the driving force for the passage of drugs in filtration
Hydrostatic or the osmotic pressure difference across the membrane
47
What type of drugs normally undergo filtration
Water-soluble drugs e.g. urea, water & sugars, renal excretion, removal of drug from CSF & entry of drug into the liver
48
How can motility affect drug absorption
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
Where are most drugs absorped
Small intestine
50
How can food affect drug absorption
Can enhance or impair rate of absorption
51
How can illness affect drug absorption
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
How are most drugs given
Orally
53
What is first pass metabolism
Metabolism of drug prior to reaching systemic circulation
54
Where can first pass metabolism occur
``` Gut lumen (acid, enzymes) Gut wall (metabolic enzymes) Liver (hepatic enzymes) ```
55
Which factors should be considered when administering drugs using subcutaneous/intramuscular methods
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
What is sublingual absorption
Under the tounge
57
How does sublingual absorption work
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
Describe rectal administration
Drugs given via the rectum bypass first pass metabolism | Absorption tends to be slow
59
Why are some drugs administered through the rectum
Rectum is often used for drugs which cause irritation of the stomach
60
What is inhalation/nasal administration dependent on
Type of delivery system, particle size, patient technique
61
What are the advantages of inhalation/nasal administration
Better for volatile agents Can be metabolism in lungs Relatively rapid action
62
What are the disadvantages of inhalation/nasal administration
About 5-10% absorbed
63
When is inhalation/nasal administration normally used
For topical effect | To avoid problems of oral absorption (e.g. nausea)
64
Describe transdermal administration
Avoids first pass metabolism Can provide controlled release Few substances well absorbed Need to be non-irritant
65
What needs to be considered when deciding for the mode of administration
``` 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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