Drug Absorption Flashcards Preview

Principles of Disease > Drug Absorption > Flashcards

Flashcards in Drug Absorption Deck (32):
1

Pharmaceutical process

get the drug into the patient

2

Pharmacokinetic process

get the drug to the site action

3

Pharmacodynamic process

produce the correct pharmacological effect

4

Therapeutic process

produce the correct therapeutic effect

5

What are the 4 basic factors that determine drug pharmacokinetics?

-absorption
-distribution
-metabolism
-elimination

6

What does ADME enable us to understand?

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

7

Absorption

-the process of movement of unchanged drug from the site of administration to the systemic circulation
-there is always a correlation between plasma concentration of a drug and the therapeutic response

8

How can drugs be absorbed?

-oral
-IV
-IM
-other GI- sublingual, rectal
-inhalation
-nasal
-transdermal

9

What are important issues to consider with oral absorption?

-amount of drug which enters the systemic circulation
-speed at which this happens

10

What is Tmax?

-the time to peak concentration
-the more rapid the rate of absorption, the earlier the drug concentration peak

11

What is Cmax?

-peak concentration
-increasing dose does not affect the time at which peak concentration is reached but does increase peak concentration

12

What is AUC?

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

13

Therapeutic range

a drug is active over a range of concentrations

14

What happens outwith the therapeutic range?

-below this there will insufficient or no pharmacological action
-above this toxicity occurs

15

Therapeutic index

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

16

Bioavailability

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

17

What method of administration has 100% bioavailability?

IV

18

Factors affecting bioavailability

-formulation
-ability of the drug to pass physiological barriers
-gastrointestinal effects
-first pass metabolism

19

How can drugs be transported across membranes?

-passive diffusion
-filtration
-bulk flow
-active transport
-facilitated diffusion
-ion-pair transport
-endocytosis

20

What is the degree of ionisation of a drug dependent on?

environment

21

What will happen to the un-ionised form of the drug?

It will cross the membrane and should distribute across the membrane until equilibrium is reached- an equal concentration at each side

22

What is ion trapping?

an acidic drug will be more concentrated in the compartment with high pH

23

What is the Henderson Hasselbalch equation?

the relationship between the local pH and the degree of ionisation

24

What is the result of the Henderson Hasselbalch equation?

small changes in pH may significantly influence the ionisation of a drug and so the rate of absorption or diffusion

25

Aspirin is a weak acid, so should be absorbed more easily from the stomach. Why is it not?

-There may be more important factors such as available gut surface are, so in fact aspirin is more absorbed from the small intestine. Even though it is ionised and less lipid soluble.

26

What must a drug be to pass across a lipid layer?

-in solutions
-lipid soluble

27

How is the ability of a drug to diffuse across a lipid barrier expressed?

lipid-water partition coefficient

28

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

29

Compare the diffusion of lipid soluble vs not lipid soluble.

-a drug that is highly lipid soluble will rapidly diffuse across a cell membrane- reach the brain, ovaries, testes and liver
-a drug that is not lipid soluble may not be absorbed at all, for example gentamicin

30

What must be true of the drugs fro them to undergo active transport?

they must resemble naturally occurring compounds

31

Where does filtration usually occur?

through channels in the cell membrane

32

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

hydrostatic or the osmotic pressure difference across the membrane