Drug Absorption

Question 1

What is the pharmaceutical process?

Answer 1

Producing the drug - so basically getting the drug into the patient

Question 2

What is the pharmacokinetic process?

Answer 2

getting the drug to the site of action - basically what the body does the drug

Question 3

What is the pharmacodynamic process?

Answer 3

producing the correct pharmacological effect - what the drug does to the body

Question 4

What is the therapeutic process?

Answer 4

producing the right therapeutic effect

Question 5

What are the four basic factors what determine the pharmacokinetics of a drug?

Answer 5

absorption, distribution, metabolism, elimination

ADME

Question 6

What does the pharmacokinetics allow understanding of?

Answer 6

dosage, drug administration, drug handling, patient variability, potential for harm

Question 7

Why is it important to have a good understanding of a drug’s pharmacokinetics?

Answer 7

to individualise patient drug therapy, monitor mediations with a narrow therapeutic index and decrease the risk of adverse effects whilst maximising pharmacological response of medications

Question 8

To have biological action where must must drugs enter and be distributed to?

Answer 8

enter bloodstream

distributed to site of action

Question 9

What are the different ways drugs can be taken?

Answer 9

orally
intravenously 
subcutaneously 
intramuscularly 
sunlingually
rectally
inhaled
transdermally
nasally

Question 10

Are intravenous drugs absorbed? and why are they more dangerous?

Answer 10

no - injected straight into blood

more dangerous if allergic or wrong dose as immediately in blood

Question 11

What is subcutaneous administration? Give an example of a drug administered in this way.

Answer 11

Injection under skin

insulin

Question 12

What is intramuscular administration? Give an example of a drug administered in this way.

Answer 12

Deep into muscle

Hep B vaccine

Question 13

What is sublingual administration? Give an example of a drug administered in this way.

Answer 13

Under the tongue - absorption from buccal mucosa
angia medication (e.g. GTN) - useful as it bypasses the liver so doesn't get metabolised

Question 14

What does transdermal administration of a drug normal involve?

Answer 14

medicated adhesive patch that is placed on skin and delivers set amount of mediation
avoids first pass metabolism

Question 15

What is absorption?

Answer 15

Absorption is defined as the process of movement of unchanged drug from site of administration to the systemic circulation

Question 16

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

Answer 16

Therapeutic response

Question 17

What are the important factors when it comes to oral absorption?

Answer 17

amount of drug which enters the systemic circulation

speed at which it happens

Question 18

Define Tmax and explain how it is important.

Answer 18

Tmax = the time to peak concentration of a drug

important when you need to treat something quickly, you want it to get to a therapeutic range quickly

Question 19

Define Cmax and explain how it is important.

Answer 19

Cmax = peak concentration

Want to make sure it is in a therapeutic range but not toxic

Question 20

What does a higher Tmax mean?

Answer 20

An earlier drug concentration peak, so more rapid absorption taking place

Question 21

Cmax would only be increased under what circumstances?

Answer 21

if dose increased

Question 22

What is the AUC and what does it relate to?

Answer 22

Area under the drug concentration-time curve

represents total amount of drug which reaches the systemic circulation

Question 23

What is the therapeutic range?

Answer 23

range of concentrations over which a drug is active

Question 24

What is the therapeutic index?

Answer 24

the range over which a drug is active and safe (above this drug toxicity occurs, below this drug is inactive)

Question 25

What does the AUC allow estimation of?

Answer 25

the amount of drug that reaches the circulation and is available for action

Question 26

What is the bioavailability of a drug?

Answer 26

The proportion of the drug that enters the circulation and so can have an active effect

Question 27

What is the bioavailability of an IV drug?

Answer 27

100%

Question 28

What are the factors affecting bioavailability in oral absorption?

Answer 28

``` Formulation (e.g. slow release preparations) ability of drug to pass physiological barriers (dependent on particle size, lipid solubility, pH and ionisation) gastrointestinal effects (gut motility, food, illness) first pass metabolism ```

Question 29

What ways can a drug pass across membranes?

Answer 29

``` passive diffusion (if lipid soluble and small enough) filtration bulk flow active transport facilitated diffusion ion-pair transport endocytosis ```

Question 30

Do drugs ionise in water?

Answer 30

most drugs do not completely ionise in water | as most drugs are weak acids or bases, the degree of ionisation depends on the pH of the environment

Question 31

Will ionised or unionised forms of a drug be present in the body, which would pass the cell membranes?

Answer 31

Both forms present Ionised drug will not pass membrane the unionised form should distribute across the membrane until equilibrium is reached - equal conc at both sides

Question 32

An acidic drug will be more concentrated in the compartment with high pH due to what?

Answer 32

ion trapping

Question 33

Small changes in pH do what to the ionisation of a drug and its absorption/diffusion?

Answer 33

small influences in pH greatly influence the ionisation of a drug and so the rate of absorption or diffusion

Question 34

To pass a lipid bilayer what must a drug be?

Answer 34

in a solution and be lipid soluble

Question 35

What is a lipid-water partition coefficient?

Answer 35

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

Question 36

Give an example of a drug that is non lipid soluble and as a result is not absorbed at all.

Answer 36

Gentamicin

Question 37

What does the passive diffusion of a drug across a membrane depend on?

Answer 37

lipid solubility and degree of ionisation

Question 38

Active Absorption

Answer 38

relatively unusual e.g.s iron, K, Na, Ca uptake of levodopa by brain energy dependent to undergo most drugs resemble naturally occurring compounds drug is reversibly bound to a carrier system

Question 39

Where does filtration normally occur? And with what kind of substances?

Answer 39

in channels in cell membrane | low molecular size (smaller than diameter of pore) molecules

Question 40

What is the driving force for filtration?

Answer 40

Hydrostatic or osmotic pressure difference across the membrane

Question 41

How can gut motility affect drug absorption?

Answer 41

speed of gastric absorption affects speed at which drug reaches site of action can be affected by other drugs, food/drink, illness

Question 42

How can illness affect drug absorption?

Answer 42

malabsorption (eg Coeliac disease) can increase or decrease rate of absorption migrane reduces rate of stomach emptying and therefore rate of absorption of analgesic drugs e.g. c. diff treated w/ vancomycin - altered lining of bowel so drug can be absorbed in bowel

Question 43

What is first pass metabolism?

Answer 43

Metabolism of the drug prior to reaching systemic circulation can be a limit on oral route for some drugs, e.g. insulin can't be taken orally

Question 44

Where are the sites that first pass metabolism can take place?

Answer 44

``` Gut lumen (acid, enzymes) gut wall (metabolic enzymes) liver (hepatic enzymes) factors can be changed by other drugs and disease ```

Question 45

What does first pass metabolism vary between?

Answer 45

varies between different people

Question 46

Subcuntaneous/intramuscular depend on what and avoid what?

Answer 46

depend on blood flow to site (only need small volume) avoids first pass metabolism not all drugs can be given in this way

Question 47

Rectal absorption tends to be slow, but when is it used?

Answer 47

for drugs that cause irritation of the stomach

Question 48

What are important considerations for the mode of administration?

Answer 48

``` 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 ```