Lecture 11

Question 1

What is excretion?

Answer 1

The process whereby compounds are removed from the body to the external environment

Question 2

What are the sites of drug excretion?

Answer 2

The kidney which is the most important site of drug excretion
Biliary excretion which is typically used for drugs with a high molecular weight
Lungs which are only really used for volatile gases

Question 3

What are the general features of the kidney?

Answer 3

Plays a significant role in regulating volume and composition of body fluids
Conserves essential substances and removes waste products
has many specialised transport systems
removes H2O soluble drugs and metabolites

Question 4

What are the three steps of drug excretion by the kidney?

Answer 4

1. Glomerular filrtation of unbound drug (130mL/min,20% plasma flow)
2. Active secretion of both free drug and protein bound drug by transporters
3. Filtrate concentrated in the tubules may generate a favourable concentration gradient to cause some drugs to be reabsorbed

Question 5

What are the factors which influence renal drug excretion?

Answer 5

Gender (femals have 80% renal function of males)
Age (renal function declines with age)
Pregnancy (renal function increases during pregnancy)
Some diseases may have effects

Question 6

What is the relationship between renal function and renal drug excretion?

Answer 6

A decrease in renal function will result in a decrease in drug excretion

Question 7

How can the renal excretion of drugs be altered?

Answer 7

Competitive inhibition of tubular secretion
pH changes
Influence of urinary flow rate

Question 8

How do pH changes alter renal excretion of drugs?

Answer 8

Things such as sodium bicarbonate can be taken to alkalinize the urine resulting in the ionisation of weak acids leading to increased acid secretion
Ammonium chloride can be used to acidify the urine to enhance basic drug excretion through the same mechanism