Pharmacology- Drug Elimination Flashcards
Where are water and most electrolytes reabsorbed?
In the renal tubules
How is most drug elimination mostly accomplished?
renal filtration of blood plasma
What happens to drug metabolites which are rendered polar and water soluble by phase 2?
they are not reabsorbed; instead, they are excreted by urine
Clearance (CL)
volume of blood removed of a drug per unit time
it is a flow parameter
Which 3 components can CL of a drug be broken down into?
Renal clearance (CLr) Hepatic clearance (CLh) Other elimination routs (CLo)
Why is CL important?
it helps determine the dosage rate needed to maintain a desired [D]plasma
distinguish CL and Vd
They are INDEPENDENT of one another
both determine the elimination half life of a drug
CL equation
CL= rate of drug elimination/ [drug]plasma
Vmax
the maximum rate of drug elimination
Km
drug concentration at which the rate of elimination is half Vmax
Michaelis-Menten kinetics equation
Re=Vmax x [Drug]plasma/ Km + [drug]plasma
When does a steady state exist?
When rate of drug administration (R0)= rate of drug elimination (RE)
Elimination half life (t1/2)
depends on Vd and CL
= 0.693 x Vd/ CL
Determines time required for SS to be achieved and for drug to be eliminated from the body
Effect of ageing on t1/2
decreases muscle mass-> Vd decreases-> t1/2 decreases
Effect of obesity on t1/2
increase in adipose tissue-> increase in Vd-> increase in t1/2
