Drug Distribution Flashcards
what causes a drug to be more extensively spread around the body?
a higher volume of distribution
what are the three main compartments that the drug is distributed into?
vascular, extracellular and intracellular
how is heparin only able to stay in the vascular compartment?
is a large molecule so cannot penetrate the capillary
how is ethanol able to access all compartments?
very small molecules and lipid soluble
what happens to the drug if they bind highly to plasma proteins?
they stay in the vascular compartment
what is the definition of the volume of distribution?
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
how do you calculate the volume of distribution?
the dosage/the concentration in the plasma
what can be said if the volume of distribution is higher than 42 litres?
this is higher than the water content of the body so the drug has been stored in tissue reservoirs
how does plasma protein biding affect distribution?
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
what are some examples of drugs that are limited by plasma protein binding?
albumin and alpha 1 acid glycoprotein
how is the ratio of free to bound drugs maintained?
when the amount of free drug decreased, more of the bound drug dissociates and replaces the free drug via diffusion
what affect does aspirin have on warfarin?
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
what type of drugs will especially seep into adipose tissue?
highly lipid soluble drugs such as anaesthetics
what causes the effects of drugs to be longer in overweight patients?
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
what should be done to the dosage in obese patients? what effect does this have?
increased as they will have a larger volume of distribution, yet the effects of the drug will be longer lasting
how does tissue binding affect the effects of some drugs?
has the potential to turn short term effects into long term effects
what are examples of drugs that have longer lasting effects due to tissue distribution?
Tetracycline and chloroquine
how are the effects of tetracycline prolonged?
binds to calcium so accumulates in teeth and bone
how are the effects of chloroquine prolonged?
attaches to the liver, kidney, lungs and spleen and also the retina due to binding to melanin-containing cells
what are continuous capillaries?
have a continuous endothelial membrane and basal lamina
what are fenestrated capillaries?
have a fenestrated endothelial lining yet a complete basal lamina
what are discontinues capillaries?
they have an incomplete endothelial membrane and basal lamina and so this causes an intercellular gap
what is an astrocyte?
star shaped glial cells which have foot process which bind to the outside of the capillary
what causes the blood brain barrier in capillaries?
tight junctions between the endothelial cells which prevents the passage of substances and the astrocytes form an extra layer around the capillary
what properties must a molecule have to pass through the blood-brain barrier?
be small and lipid soluble
how might a larger or polar molecule be able to pass through the blood-brain barrier?
via a carrier molecule
what is the purpose of the blood-brain barrier?
to maintain homeostasis and create a barrier against infection, while still being accessible to certain nutrients
what reduces the diffusion of drugs into the placental membrane?
several layers of cells that separate the maternal and foetal circulation
what makes the placental barrier ineffective?
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
