Drug Distribution

Question 1

what causes a drug to be more extensively spread around the body?

Answer 1

a higher volume of distribution

Question 2

what are the three main compartments that the drug is distributed into?

Answer 2

vascular, extracellular and intracellular

Question 3

how is heparin only able to stay in the vascular compartment?

Answer 3

is a large molecule so cannot penetrate the capillary

Question 4

how is ethanol able to access all compartments?

Answer 4

very small molecules and lipid soluble

Question 5

what happens to the drug if they bind highly to plasma proteins?

Answer 5

they stay in the vascular compartment

Question 6

what is the definition of the volume of distribution?

Answer 6

the volume of fluid required to contain the total amount of the drug in the body at the same concentration at that present in the plasma

Question 7

how do you calculate the volume of distribution?

Answer 7

the dosage/the concentration in the plasma

Question 8

what can be said if the volume of distribution is higher than 42 litres?

Answer 8

this is higher than the water content of the body so the drug has been stored in tissue reservoirs

Question 9

how does plasma protein biding affect distribution?

Answer 9

if the drug binds to a large plasma protein this means it cannot penetrate certain membranes and so determines the volume of distribution of the drug in the body

Question 10

what are some examples of drugs that are limited by plasma protein binding?

Answer 10

albumin and alpha 1 acid glycoprotein

Question 11

how is the ratio of free to bound drugs maintained?

Answer 11

when the amount of free drug decreased, more of the bound drug dissociates and replaces the free drug via diffusion

Question 12

what affect does aspirin have on warfarin?

Answer 12

aspirin displaces warfarin from the plasma proteins and causes more of the drug to be free and therefore increases its anti-coagulant effects in the blood as more can access the liver

Question 13

what type of drugs will especially seep into adipose tissue?

Answer 13

highly lipid soluble drugs such as anaesthetics

Question 14

what causes the effects of drugs to be longer in overweight patients?

Answer 14

because they will have more adipose tissue and so after the drug is excreted from the CNS, the adipose tissue will still have drug present

Question 15

what should be done to the dosage in obese patients? what effect does this have?

Answer 15

increased as they will have a larger volume of distribution, yet the effects of the drug will be longer lasting

Question 16

how does tissue binding affect the effects of some drugs?

Answer 16

has the potential to turn short term effects into long term effects

Question 17

what are examples of drugs that have longer lasting effects due to tissue distribution?

Answer 17

Tetracycline and chloroquine

Question 18

how are the effects of tetracycline prolonged?

Answer 18

binds to calcium so accumulates in teeth and bone

Question 19

how are the effects of chloroquine prolonged?

Answer 19

attaches to the liver, kidney, lungs and spleen and also the retina due to binding to melanin-containing cells

Question 20

what are continuous capillaries?

Answer 20

have a continuous endothelial membrane and basal lamina

Question 21

what are fenestrated capillaries?

Answer 21

have a fenestrated endothelial lining yet a complete basal lamina

Question 22

what are discontinues capillaries?

Answer 22

they have an incomplete endothelial membrane and basal lamina and so this causes an intercellular gap

Question 23

what is an astrocyte?

Answer 23

star shaped glial cells which have foot process which bind to the outside of the capillary

Question 24

what causes the blood brain barrier in capillaries?

Answer 24

tight junctions between the endothelial cells which prevents the passage of substances and the astrocytes form an extra layer around the capillary

Question 25

what properties must a molecule have to pass through the blood-brain barrier?

Answer 25

be small and lipid soluble

Question 26

how might a larger or polar molecule be able to pass through the blood-brain barrier?

Answer 26

via a carrier molecule

Question 27

what is the purpose of the blood-brain barrier?

Answer 27

to maintain homeostasis and create a barrier against infection, while still being accessible to certain nutrients

Question 28

what reduces the diffusion of drugs into the placental membrane?

Answer 28

several layers of cells that separate the maternal and foetal circulation

Question 29

what makes the placental barrier ineffective?

Answer 29

drugs that have been well absorbed after oral administration can also pass the blood-brain barrier and therefore the placental barrier as readily allows the access of lipid soluble drugs