Bioavailability Tutorial

Question 1

Define excipient

Answer 1

Other material added to a drug before prescription

Question 2

Define formulation

Answer 2

Process in which different chemical substances are combined to produce a final medicinal product

Question 3

Define bioequivalence

Answer 3

Evidence the new “generic” product behaves sufficiently similar to the original to be substituted for it without causing clinical problems

Question 4

Give an advantage and disadvantage of oral admission

Answer 4

Permits self medication

Undergo extensive first pass metabolism

Question 5

Give an advantage and disadvantage of IV admission

Answer 5

Rapid onset

Trained personal required

Question 6

Give an advantage and disadvantage of inhalational admission

Answer 6

Huge surface area of alveolar membranes for absorbtion

Possible localised effect in lung

Question 7

Give an advantage and disadvantage of IM admission

Answer 7

High blood flow, increased in exercise, enables depot therapy
Possible infection + nerve damage

Question 8

Give an advantage and disadvantage of SC admission

Answer 8

Local administration, dissemination can be minimised for local effect
Possible pain

Question 9

Give an advantage and disadvantage of percutaneous admission

Answer 9

Local application + action

Local irritation + skin reactions

Question 10

Give 3 reasons why excipients are added to a drug formulation

Answer 10

To aid manufacture of the medicine
To improve chemical + biological stability
Increase acceptability to the patient by improving flavour, fragrance or appearance

Question 11

How can the physiochemical characteristics, GI pH, transportation, gastric motility, particle size and GI interaction effect bioavailability?

Answer 11

Ratio of ionised: unionised effects bioavailability + movement through the body
pH effects ionisation state
Active transport requires energy, thus if lacking ATP, less drug will be bioavailable
Increased gut motility increases absorption
Smaller particles are absorbed more easily
Gut contents may interact with the drug making it inactive/ competing for its target site

Question 12

What is the therapeutic window?

Answer 12

Range of doses between minimum effective concentrations to the minimum toxic concentration

Question 13

What is the therapeutic index?

Answer 13

Comparison of amount of a therapeutic agent that causes therapeutic effect to the amount that causes toxicity.

Question 14

How can good bioavailability be achieved for drugs that undergo extensive first-pass metabolism?

Answer 14

Parenteral administration e.g. IV

Question 15

Under what circumstances could a drug, which undergoes 100% first pass metabolism, be therapeutically useful?

Answer 15

For a pro-drug where metabolism is required to liberate the active form of the drug