Pharmacokinetics- Distribution Flashcards
1
Q
What is bulk flow?
A
- When the drug in the bloodstream distributes drugs passively to major organs, depending on perfusion
2
Q
What is perfusion?
A
Blood flow to each organ
3
Q
What is drug distribution?
A
The reversible transfer of a drug between the blood and extravascular tissues of the body
4
Q
Describe drug distribution after an intravenous dose
A
- IV dose distributed through blood circulation very rapidly, then to organs depending on plasma protein binding, tissue perfusion and drug permeability
5
Q
What is plasma protein binding?
A
- Many drugs bind reversibly to plasma proteins (permeability)
- Whilst bound, it cannot be active or leave circulation, increases duration and slows down distribution
- Temporary storage compartment
- Displaceable
- As drug plasma levels fall, more of bound drug released from complex
6
Q
How is the extent of drug distribution estimated?
A
- Marker substance, allowing to distribute-testing concentration
- Assumption that there will be an even distribution
7
Q
What is the significance of body compartments in drug distribution?
A
- Drugs may distribute into 1 or more body compartments
- Provided even distribution, extent of dilution of a sample indicates the volume of distribution
8
Q
What do Vd values mean?
A
- Volume of distribution- the volume of body fluids into which a drug appears to have been distributed to
- Fixed characteristic and independent of drug dose
- Lites, corrected to litres.kg
9
Q
What is ‘apparent Vd’?
A
- If drug not evenly distributed, Vd may be deceptive
- Some drugs appear to have impossibly Vds
- Plasma conc. does not reflect the local tissue, it only appears low
10
Q
Describe the blood-brain barrier
A
- Tight junctions and astrocytes
- Capillaries in brain have thicker walls, increasingly difficult for drugs to exit circ.
- Privileged space that excludes large drug molecules and water-soluble drugs
11
Q
What does the blood-brain barrier allow access to?
A
- Small lipid-soluble drugs
12
Q
In what instances would the blood-brain barrier be deficient?
A
- Foetus/new-borns
- Those with meningitis
