Bioavailability

Question 1

What does bioavailability mean?

Answer 1

Fraction of a dose that reaches the systemic circulation unchanged.
fraction absorbed and metabolised prior to the circulation
= known as ‘f’

Question 2

What is the bioavailability via the intravenous route?

Answer 2

F = 1

fraction of dose which reaches the systemic circulation remains unchanged.

Question 3

What is the bioavailability via the enteral route?

Answer 3

F = less than 1

Question 4

Why is the bioavailability via the enteral route less than 1?

Answer 4

Some of the drug will be lost through the passage straight through the GI tract.
Known as pre - systemic metabolism.

Question 5

What does the site of absorption determine?

Answer 5

Determines the extent of metabolism which occurs prior to the drug entering the systemic circulation.

Question 6

What is the bioavailability of parenteral route (non - IV)?

Answer 6

F will be less than one BUT it is higher than the enteral route.

Question 7

What are the drug factors which affect F?

Answer 7

Concentration
Formulation
Molecular Size
Other drug properties (lipid solubility / acid - base status)

Question 8

What are the patient factors which affect F?

Answer 8

Blood Supply
Motility
Absorption Surface
Gastric Content
Bile
Enteric Bacteria

Question 9

Why can a large dosage have an affect on F?

Answer 9

Higher concentration gradient thus there is a faster rate of absorption.