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16 Cards in this Set
- Front
- Back
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drug elimination
the total drug elimination is the sum of: |
metabolism of drugs
- in liver - in other tissues excretion of drugs - in kidney (filtration, active secretion, reabsorption) - in bile - in expired air - in feces... |
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drug metabolism
the drug in tissues is distributed between: |
membranes
aqueous phases (extra and intra) |
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the metabolizing enzymes can be bound to membranes or dissolved in:
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the aqueous phases.
* the active sites are in contact with water |
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only the free drug molecules which are present in aqueous phases can be metabolized.
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true
accumulation of drugs in membranes and binding to proteins prevent them from metabolism. |
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drug fates in tissue
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see slide
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binding to enzymes and other proteins is practically :
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instantaneous
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to simplify the description of the system, how many assumptions are required?
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three
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assumption I
linear protein binding |
drugs are usually applied in low concentrations and protein binding is far from saturation (linear binding)
see slide |
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assumption 2
first-order enzymatic metabolism |
drugs are usually applied in concentrations and the rate of metabolism is far from saturation
(linear process) Michaelis-Menten kinetics Vm is not related to membranes it is max rate of variation Km is MM constant see slides |
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assumption 3
first order reactions hydrolysis |
D + H2O ---> M + byproduct
the rate equation reads: dc/dt = k * ch2o * c = kh * c since ch2o = const and kh = k * ch2o hydrolysis is practically a first order reaction |
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because the drug concentration is usually much lower than that of the other reactant (AA, glutathion...):
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the reactions of the drug molecules are of the first order
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decription of metabolism in tissue I
the total loss of drug due to metabolism dnm is: |
see slide
the sum of the drug amounts metabolized in individual cells by spontaneous and enzymatic reactions |
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description of metabolism in tissue II
sum up of spontaneous and enzymatic rxn rates |
spontaneous
k * ca enzymatic vm * em/km * ca |
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description of metabolism in tissue III
the cells differ in: |
- the content of reactants (hidden in ki)
- enzymes (emi) - and in the volume Vi see slide |
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description of metabolism in tissue IV
the loss of drug due to metabolism is: |
the sum of amounts metabolized in individual cells
see slide |
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description of metabolism in tissue V
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see slide
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