Bioavailability

Question 1

What is bioavailability?

Answer 1

The fraction of a dose that reaches the systemic circulation unchanged.
This is also known as ‘F’

Question 2

Bioavailability via the intravenous route

Answer 2

Fraction of a dose that reaches the systemic circulation unchanged. F = 1

Question 3

Bioavailability via the enteral route

Answer 3

Some of the drug will be lost through passage straight through the GI tract (pre-systemic metabolism)
F = less than 1

Question 4

Patient factors that affect F:

Answer 4

Motility = rate at emptying of gastric content
Blood supply
Absorption surface 
Gastric content 
Bile
Enteric bacteria

Question 5

Drug factors affecting F:

Answer 5

Concentration
Formulation
Molecular size
Drug properties

Question 6

How is bioavailability measured?

Answer 6

The area under the curve

Question 7

What is the bioavailability of the parenteral route?

Answer 7

F = less than 1 but higher than the enteral route

This is not the same as IV

Question 8

Examples of transdermal administration:

Answer 8

Nicotine patches

Lidocaine patches

Question 9

Why does a higher drug dose affect bioavailability ?

Answer 9

There’s a greater concentration gradient so there is a faster rate of absorption.