Pharmacokinetics II (Drug Elimination & Multiple Dosing) Flashcards
What is the basis of the maintenance dose?
Replacing the amount of drug cleared from the body after the previous drug administration.
How many half lives does it take to achieve steady-state?
Four-six
Relation of time to dosage in steady-state
There is none
Fluctuations are proportional to what?
Dosage interval and half-life of the drug
How are fluctuations blunted?
By slow absorption
Define first-order elimination
Elimination rate of the drug is a constant fraction of the drug remaining in the body rather than a constant amount cleared per unit time
Define zero-order elimination
Independent of the total concentration of drug in the body; a fixed amount will be metabolized per unit time
More drugs used clinically obey __-order kinetics.
first
Zero-order kinetics are seen more in what drugs?
Ones that are eliminated primarily by metabolism rather than excretion
What is the basis for the linear decrease in drug concentrations?
Saturation of metabolic pathways
Hepatic clearance is determined by which three factors?
Hepatic blood flow
Plasma protein binding
Intrinsic clearance
What happens with restrictive hepatic clearance?
Flow is much higher than clearance (low extraction), so there is not much first pass metabolism
In restrictive hepatic clearance, what change will have the greatest effect on clearance?
Binding or metabolism activity will have a greater effect than changes in blood flow
Examples of drugs undergoing restrictive hepatic clearance
Warfarin, phenytoin
Non-restrictive hepatic clearance
Drugs have high hepatic extraction (Q
