Drug Absorption Flashcards Preview

Principles of Disease > Drug Absorption > Flashcards

Flashcards in Drug Absorption Deck (44):
1

Define Pharmaceutical process

Get the drug into the patient

2

Define Pharmacokinetic process

Get the drug to the site of action

3

Define Pharmacodynamic process

Produce the correct pharmacological effect

4

Define Therapeutic process

Produce the correct therapeutic effect

5

What determines drug pharmacokinetics

Absorption
Distribution
Metabolism
Elimination

6

What are the methods of administration?

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

7

What is absorption?

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

8

What does ADME allow?

understanding of:
Dosage
Drug administration
Drug handling
Patient variability
Potential for harm.

9

What is sublingual?

Under the tongue

10

What is Tmax? Oral absorption

The time to peak concentration, important in relieving pain

11

What is Cmax? Oral absorption

The peak concentration, important in determining a toxic dose

12

What is the (AUC)? Oral absorption

The area under the drug concentration-time curve

13

Does the dose effect the tmax?

No, alters cmax

14

What does the The area under the drug concentration-time curve represent?

The amount of drug which reaches the systemic circulation

15

What is the Theraputic range?

The range of concentrations at which a drug is active.

16

What happens above or below the theraputic range

Toxicity

Insufficient pharmalogical action

17

What does The AUC allows us to estimate?

The amount of drug which reaches the circulation and which is available for action
BIOAVAILABILITY - Used to compare routes of administration

18

What is the bioavailability of an intravenous drug?

100%

19

What are the factors affecting Bioavailability? (oral absorption)

Formulation -
Slow release preparations

Ability of drug to pass physiological barriers
-Particle size
-Lipid solubility
-pH and ionisation

Gastrointestinal effects
-Gut motility
-Food
-Illness

First pass metabolism (whereby the concentration of a drug is greatly reduced before it reaches the systemic circulation.)

20

What is dissolution?

The rate a drug breaks up

21

What is an example of a physiological barrier?

Transport across membranes

22

What are the methods of transport across membranes?

Passive diffusion
Filtration
Bulk flow
Active transport
Facilitated diffusion
Ion-pair transport
Endocytosis

23

What does the degree of the ionisation of the drug depend on?

As most drugs are weak acids or bases the degree of ionisation depends on the pH of the environment

24

What form of the drug crosses the membrane?

The unionised form

25

What is the distribution of the un-ionised form of a drug?

Should distribute across the membrane until equilibrium is reached - equal concentration on each side.

26

Where will an acidic drug be most concentrated?

In the compartment with high pH

27

What does the Henderson-Hasselbalch equation describe?

The relationship between the local pH and the degree of ionisation

28

What is The ability of a drug to diffuse across a lipid barrier is expressed as?

lipid-water partition coefficient

29

What is the lipid-water partition coefficient?

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

30

Describe passive diffusion

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

31

Describe Active Absorption

Relatively unusual.
Occurs against concentration gradient.
Requires carrier and energy.
Specific
Saturable.
Iron ,K , Na , Ca
Uptake of levodopa by brain

Energy dependant

32


What is the structure of drugs that undergo active transport?

They must resemble naturally occurring compounds

33

Describe facilitated diffusion

Occurs along the concentration gradient
Require carriers
Saturable
Structure specific
No energy required
Mixed order kinetics
monosaccharides, amino acids, vitamins

34

Where does filtration occur?

Through channels in the cell membrane.

35

What is the milecular size of the drug in Filtration / Bulk Flow/ Pore Transport?

Low molecular size

36

What is the driving force in Filtration / Bulk Flow/ Pore Transport?

Hydrostatic or the osmotic pressure difference across the membrane.

37

What does the speed of gastric absorption affect?

speed at which drug reaches site of absorption

38

What is the effect of food on absorption?

Can enhance or impair rate of absorption

39

How does illness affect absorption?

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

40

Decribe the Subcutaneous / Intra-muscular route of administration?

Needs small volume

Avoids first pas metabolism

41

Describe Sublingual, Buccal administration

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

42

Describe rectal administraion

Bypass first pass metabolism.

Absorption tends to be slow.

The rectum is often used for drugs which cause irritation of the stomach.

43

Describe the benefits of inhalation/nasal administration

Relatively rapid action

Avoids problems with oral absorption

Although only 5-10% absorbed

44

Describe Transdermal absorption

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