what are the main organs of drug elimination and by what mechanism
- kidneys
- renal filtration of blood plasma
what is reabsorbed during renal filtration and what isn’t
- water and electrolytes absorbed
- polar drug metabolite not
clearance
expression of the elimination of drug from the body - vol cleared per unit time
`what can clearance be broken down into
hepatic (Clh), renal (Clr) and other (Clo) or total (Clt)
what does clearance help to determine
dosage to maintain desired plasma conc. of drug
equation for determining clearance
Cl = rate of elimination / drug plasma conc.
first-order kinetics
as drug plasma conc. increases so to does rate of elimination
zero-order kinetics as
elimination mechanisms become saturated at Vmax
Vmax
max elimination rate
steady state
rate of drug administration = rate of elimination (inout= output)
equation for dosage rate
dosage rate = drug plasma conc. x clearance
elimination half life
time taken for drug conc. to decrease by half
steady state takes the same amount of time to reach as what
time for drug to be completely washed out of the body
what does elimination half life help determine
the time taken to reach steady state and time drug takes to be eliminated from the body
steady state usually take how many oral doses to reach
5
equation for elminiation half life
t1/2 = 0.693 x Vd / Cl
when clearence increases/decreased what happens to elimination half life
- decrease
- increase
what effects do - ageing - obesity - pathological fluid have on elimination half life and why
- decrease in muscle mass so decrease in t1/2
- increase in adipose tissue so increase in t1/2
- increase in t1/2
what effects do - CP450 induction - CP450 inhibition - cardiac/hepatic/renal failure have on elimination half life
- decrease
- increase
- increase
