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Flashcards in drug distribution Deck (39):
1

what must a drug do after it has been absorbed?

it must be available for biological action and distribution to tissues

2

what conditions must be met for a drug to become active?

drug must leave the bloodstream and enter the inter or intracellular spaces

3

what factors affect the way that a drug is distributed throughout tissues?

plasma protein binding
tissue perfusion
membrane characteristics
transport mechanisms
diseases
other drugs
elimination

4

what membrane characteristics can affect tissue distribution?

the blood-brain barrier
blood-testes/ovary barrier
whether the drug is lipid soluble
whether the drug is actively transported or not

5

what are some examples of plasma proteins that drugs bind to?

albumin
alpha 1 glycoprotein

6

what form of the drug is biologically active?

the unbound form

7

is binding reversible or irreversible?

reversible

8

what can change the amount of bound drug?

renal failure
hypoalbuminaemia
pregnancy
other drugs
saturability of binding

9

what percentage of the drug has to be bound for protein binding to be an important factor?

more than 90%

10

does tissue distribution have to be large or small in order for protein binding to be an important factor?

small

11

what is the apparent volume of distribution? (Vd)

the volume in which a drug seems to distribute within the body

12

what does a higher volume of distribution indicate?

a greater ability of the drug to diffuse into and through membranes

13

what should the the theoretical volume of distribution be?

40L

14

what would the Vd be if the drug stays in the extracellular fluid but cannot penetrate cells?

12L

15

what would the Vd be in a drug that is highly protein bound?

3L

16

what would the Vd be if the drug was sequestered in the extravascular lipid compartment?

>40L

17

what is clearance defined as?

the theoretical volume of fluid from which a drug is completely removed over a period of time?

18

what is clearance a measure of?

elimination

19

what is renal clearance dependent on?

concentration of drug and urine flow rate

20

what is hepatic clearance dependent on?

metabolism and biliary excretion

21

what is the half life of a drug?

the time taken for the drug concentration in the blood to decline to half of the current value

22

how is the half life calculated?

o.693Vd/Cl

23

what does the half life of a drug depend on?

volume of distribution and rate of clearance

24

what effect does prolongation of the half life of a drug have?

increases the toxicity of the drug due to a reduction in clearance or due to a large volume of distribution

25

what clinical application does knowledge of a drugs half life have?

allows us to figure out how often a drug needs to be administered

26

how many doses of a drug does it usually take for plasma levels of said drug to stabilise? (steady state)

4-5

27

what is drug elimination?

removal of active drug from the body

28

what does drug elimination determine?

length of action of the drug

29

what 2 parts is drug elimination made up of?

metabolism (usually in the liver)
excretion (usually in the kidney but also the biliary system/gut and lung)

30

what are the 3 principal mechanisms employed by the kidney with regards to drug excretion?

glomerular filtration
passive tubular reabsorption
active tubular secretion

31

when would an unbound drug NOT be filtered at the glomerulus?

if the molecular size, charge or shape is excessively large

32

what happens if the glomerular filtration rate is decreased?

clearance is reduced

33

what happens to the concentration of a drug as the filtrate moves down the renal tubule?

it increases

34

where does passive diffusion occur in the kidney?

the distal tubule and collecting duct

35

what are the only drugs that are reabsorbed in passive tubular reabsorption?

un ionised drugs

36

what kinds of drugs are actively secreted into the proximal tubule?

acidic and basic compounds

37

what kinds of drugs is active tubular secretion most important in eliminating?

protein bound cationic and anionic drugs

38

what is the term given for when drugs are reabsorbed from the bile into the circulation?

entero-hepatic circulation

39

when does entero-hepatic circulation continue until?

until the drug is metabolised in the liver or excreted by the kidneys