Biopharmaceutics Lecture 1

Question 1

Why is injection (as a route of administration) used?

Answer 1

Rapid response 
Can use drugs that would be destroyed in the GIT if taken orally 
Can use on patient groups such as:
-unconscious patients
-those who can't swallow
-those nil by mouth

Question 2

Describe the physiological surface barriers of the skin that drug from a transdermal dosage form/patch would have to cross

Answer 2

Stratum corneum (complex structure of dead cells)
Epidermis (avascular, tightly-packed living cells)

Question 3

Explain the difference between “drug” and “medicine”

Answer 3

Drug describes the pharmacological agent/therapeutic molecule/API by itself
Medicine describes the drug itself and excipients together

Question 4

What are the disadvantages for using injections to deliver drugs?

Answer 4

• less convenient compared to oral route
• cost
• stability issues e.g. Microbial contamination, short shelf life
• patient pain
• can achieve suitable rate of absorption using oral route

Question 5

Define bioavailability

Answer 5

Defined by FDA as the rate and extent to which the active ingredient is absorbed from a drug product and becomes available at the site of action.

Question 6

Out of ADME, which letters are about bioavailability?

Answer 6

Bioavailability is about absorption only

Rate and extent at which drugs reach the systemic circulation

Question 7

What is the absolute bioavailability of an IV injection?

Answer 7

100%

Question 8

Define absolute bioavailability

Answer 8

The fraction of drug that arrives in the systemic circulation

Question 9

What factors to bioavailability studies view?

Answer 9

• rate of absorption
• variables that affect rate and extent
• mechanisms involved

Question 10

In ADME, what does M refer to?

Answer 10

Metabolism i.e. All changes to the drug in the body (gut wall, liver etc)

Question 11

In the early stages of drug development, what does one focus upon?

Answer 11

Studying drug molecules in solution, interacting with isolated target cells

Question 12

In the later stages of drug development, what does one focus upon?

Answer 12

Success depends on development of a suitable dosage form

Question 13

Why don’t we just administer pure drug in solution and forget about formulation?

Answer 13

Usually too expensive to administer drug in solution

Question 14

In transdermal drug delivery systems, what is added/removed to increase subcutaneous permeability?

Answer 14

Chemical enhancers are added

Question 15

Describe the ideal properties of an API to be delivered via a TDDS

Answer 15

Low permeability
Low Mr
Lipophilic

Question 16

How does the drug get absorbed in the GIT?

Answer 16

GI absorption - High surface area due to villi and microvilli

• Transcellular transport (through cells lipid bilayer)if lipophilic molecules
• Paracellular transport (gaps between cells) if hydrophilic drugs

Question 17

Name some broad potential influences on drug availability for absorption

Answer 17

• Physiological
• Drug itself
• Dosage form

Question 18

Describe some physiological effects that can influence drug availability for absorption

Answer 18

• rate of transit
• properties of lumen fluid (pH, etc)
• tissue properties at the site of absorption and the site of action

Question 19

Describe some drug factors that can influence drug availability for absorption

Answer 19

LogP
Solubility
pKa
Pharmacological effects of the drug or other agents

Question 20

Describe some dosage form factors that can influence drug availability for absorption

Answer 20

Particle size
Size of dosage form itself
Route of administration
Disintegration rate
Dissolution rate

Question 21

Why in biopharmaceutics, does “available at the site of action” equal the same as “arrives at the systemic circulation”

Answer 21

• Practical reasons, blood is sampled easily, but tissues are not
• Pharmacokinetics- blood is the central compartment from which drug is distributed
• Absorption=process of drug going to central comportant (systemic circulation) by a route of administration
• Once drug is in the central compartment, formulation is then irrelevant as drug is dissolved in blood plasma. Formulation is only relevant when it comes to drug absorption

Question 22

Give 6 examples of drugs used in transdermal drug delivery systems

Answer 22

GTN
Nicotine
Fentanyl
Estradiol
Testosterone
Anti-nausea agents