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6 Cards in this Set

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Define Volume of distribution (Vd).
Vd is the volume of fluid that would be required to contain the drug at the same concentration as in plasma.
What are the factors contribute to the limited diffusion of water soluble materials from capillaries to brain tissues?
1. Endothelial cells of brain capillaries are more firmly joined, thus pores are smaller or non-existent
2. Brain capillaries are sheathed with processes of astrocytes
The blood brain barrier, is highly permeable in infants making them more sensitive to centrally acting drugs. What factors alter the permeability of the BBB in adults?
1. Certain disease states such as inflammation (meningitis)
2. Active transport through the choroid plexus and the CSF
What is a key difference between the maternal blood flow and placental blood flow?
There is a time lag between the drug concentration in the maternal blood and the fetal blood. The rate of maternal blood flow limits the availability of drug to the fetus. Therefore, the placenta SLOWS drug movement, but does not prevent it
Define differential distribution.
This is the binding of drugs to plasma proteins or tissues, storage of drugs by body fat, BBB, and active transport into he liver, kidney, and other organs. Therefore, the site of drug action is not necessarily the site at which drug concentration is the highest in the body
How can the redistribution of drugs influence drug action?
The initial distribution of drugs often follows distribution of blood flow to organs. Later, drugs may redistribute according to affinity for various tissues. For example, with short acting IV drugs, the drug initially distributes to organs which are rapidly perfused (brain, kidney). Then the drug redistributes to more slowly perfused organs such as muscle and adipose tissue. At the time of termination of a drug effect, the concentration of the drug may not be zero, but just below the minimal effective concentration, and is in equilibrium with the drug stored in muscle and adipose tissue.