Elimination

Question 1

What are the two ways drugs are eliminated?

Answer 1

• Metabolism (biotransformation)

- Excretion

Question 2

How does metabolism affect elimination?

Answer 2

Biotransformation by metabolism normally terminates pharmacological activity, making the drug easier to excrete.

Question 3

What are the 2 phases of metabolism?

Answer 3

• Phase I - formation of new or modified functional group of cleavage (oxidation, reduction, hydrolysis)
• Phase II - reactions involving conjugation with endogenous particles

This leads to more polar compounds with reduced lipid solubility resulting in more rapid excretion in bile or urine.

Question 4

Where does metabolism occur?

Answer 4

Enzymes involved in metabolism are present in many tissues but more concentrated at liver.

Question 5

Where does excretion occur?

Answer 5

• Kidney (renal excretion to urine)

- Liver (bile)

Question 6

What is hepatic secretion?

Answer 6

Drug is secreted into bile and excreted. It may be reabsorbed in intestine, entering enterohepatic circulation.

Question 7

What is renal excretion?

Answer 7

The primary route of drug excretion.

• Filtration in the glomerulus (network of capillaries in kidney, first stage of filtering process in formation of urine)
• Tubular secretion - separate active transport system in proximal tubular cells
• Reabsorption

Question 8

What individual variations affect metabolism and excretion?

Answer 8

• Age - decline in renal clearance, general metabolism impairment
• Renal disease
• Liver disease
• Competition with other drugs

Question 9

What affect does rate of elimination have on action of drug?

Answer 9

The slower the rate of elimination, the longer the amount of time in the body, more of an effect in CNS.