Pharmacology: Drug Clearance and Elimination

Question 1

what are the main organs of drug elimination and by what mechanism

Answer 1

• kidneys

- renal filtration of blood plasma

Question 2

what is reabsorbed during renal filtration and what isn’t

Answer 2

• water and electrolytes absorbed

- polar drug metabolite not

Question 3

clearance

Answer 3

expression of the elimination of drug from the body - vol cleared per unit time

Question 4

`what can clearance be broken down into

Answer 4

hepatic (Clh), renal (Clr) and other (Clo) 
or total (Clt)

Question 5

what does clearance help to determine

Answer 5

dosage to maintain desired plasma conc. of drug

Question 6

equation for determining clearance

Answer 6

Cl = rate of elimination / drug plasma conc.

Question 7

first-order kinetics

Answer 7

as drug plasma conc. increases so to does rate of elimination

Question 8

zero-order kinetics as

Answer 8

elimination mechanisms become saturated at Vmax

Question 9

Vmax

Answer 9

max elimination rate

Question 10

steady state

Answer 10

rate of drug administration = rate of elimination (inout= output)

Question 11

equation for dosage rate

Answer 11

dosage rate = drug plasma conc. x clearance

Question 12

elimination half life

Answer 12

time taken for drug conc. to decrease by half

Question 13

steady state takes the same amount of time to reach as what

Answer 13

time for drug to be completely washed out of the body

Question 14

what does elimination half life help determine

Answer 14

the time taken to reach steady state and time drug takes to be eliminated from the body

Question 15

steady state usually take how many oral doses to reach

Answer 15

5

Question 16

equation for elminiation half life

Answer 16

t1/2 = 0.693 x Vd / Cl

Question 17

when clearence increases/decreased what happens to elimination half life

Answer 17

• decrease

- increase

Question 18

what effects do 
- ageing 
- obesity 
- pathological fluid 
have on elimination half life and why

Answer 18

• decrease in muscle mass so decrease in t1/2
• increase in adipose tissue so increase in t1/2
• increase in t1/2

Question 19

what effects do 
- CP450 induction 
- CP450 inhibition 
- cardiac/hepatic/renal failure 
have on elimination half life

Answer 19

• decrease
• increase
• increase