Drug Elimination

Question 1

What is elimination?

Answer 1

Drugs and/or drug metabolites are excreted in the urine, faeces or bile

Question 2

What is the principle organ for elimination?

Answer 2

Kidneys

Question 3

How is elimination mostly accomplished?

Answer 3

Renal filtration

Question 4

What happens to water and most electrolytes?

Answer 4

They are reabsorbed into blood circulation in renal tubes

Question 5

What happens to drug metabolites that are rendered polar by phase 2 metabolism?

Answer 5

They are not reabsorbed so excreted in urine

Question 6

How does plasma concentration of drug affect elimination?

Answer 6

As it increases, effectiveness increases but toxicity also increases so a balance must be found

Question 7

What can happen at a high plasma drug concentration?

Answer 7

Accumulation of toxic metabolites

Increase in chance of immune response to drug

Question 8

What happens in the absorption phase of a plasma concentration-time profile after oral administration of a single dose?

Answer 8

Absorption is greater than elimination so plasma drug concentration is increasing

Question 9

What happens at the peak of a plasma concentration-time profile after oral administration of a single dose?

Answer 9

Absorption is equal to elimination

Question 10

What happens in the elimination phase of a plasma concentration-time profile after oral administration of a single dose?

Answer 10

Absorption is less than elimination so plasma drug concentration is decreasing

Question 11

What are the three phases of a plasma concentration-time profile after oral administration of a single dose?

Answer 11

Absorption
Peak
Elimination

Question 12

What is clearance an expression of?

Answer 12

The elimination of a drug from the body

Question 13

What is the definition of clearance?

Answer 13

Volume of blood cleared of drug per unit of time

Question 14

What does clearance not tell you?

Answer 14

How much drug is removed

Question 15

How can clearance be described?

Answer 15

Renal
Hepatic
Other elimination routes
Total clearance

Question 16

How is clearance useful?

Answer 16

It helps to determine the dosage ate needed to maintain a desired plasma drug concentration

Question 17

What determines the half life of a drug?

Answer 17

Clearance and volume of distribution

Question 18

How is clearance estimated?

Answer 18

CL = rate of drug elimination / plasma drug concentration

Question 19

When is the plasma concentration-time profile exhibiting first order kinetics?

Answer 19

Absorption stage

Question 20

When does plasma concentration-time profile reach zero order?

Answer 20

When elimination mechanisms become saturated and the reaction reaches Vmax

Question 21

When does a steady state exist?

Answer 21

When rate of drug administration is equal to the rate of drug elimination

Question 22

How is dosage rate calculated?

Answer 22

Plasma drug concentration x clearance

Question 23

How is elimination half-life calculated?

Answer 23

Elimination half-life = (0.693 x volume of distribution)/clearance

Question 24

What two things can elimination half-life determine?

Answer 24

Time required for plasma drug concentration to achieve steady state
How much time is required for a drug to be eliminated from the body

Question 25

In what way is elimination hal-life’s ability to determine How much time is required for a drug to be eliminated from the body useful?

Answer 25

Useful in designing a therapeutic dosing regimen

Question 26

How many half lives are required to reach a steady state or to fully eliminate a drug?

Answer 26

5