Introduction to Pharmacokinetics

Question 1

What is pharmacokinetics?

Answer 1

The study of movement of drugs within the body (what the body does to the drug)

Question 2

What is absorption?

Answer 2

How the drug gets from the site of administration to the plasma

Question 3

What 4 things affect absorption?

Answer 3

Route of administration
Blood flow at site of administration
Dose
Drug solubility

Question 4

What are the 3 main routes of administration/

Answer 4

• enteral: oral/rectal GI tract
• parenteral: IV, IM, subcutaneous
• percutaneous: inhalation, topical

Question 5

What is distribution?

Answer 5

Movement of the absorbed drug around the body and into tissues

Question 6

What 4 things affect distribution?

Answer 6

Blood flow
Lipid solubility and diffusion barriers e.g. BBB, placenta
Plasma protein binding
Tissue binding

Question 7

How does metabolism affect drugs?
Give an example of a drug 
- with active metabolites
- with toxic metabolites
- which is a prodrug

Answer 7

Usually inactivates drugs
can produce active metabolites e.g. diazepam –>nordiazepam
can produce toxic metabolites e.g. paracetamol
“prodrugs” - drug is not pharmacologically active until it is metabolised e.g. L-DOPA to treat parkinsons, only active after crossing BBB

Question 8

What is excretion?

Answer 8

The removal of unwanted substances from the body

Question 9

How are drugs excreted?

Answer 9

Kidney –>urine
Liver –> bile, enterohepatic circulation, prolongs extent of drug in body
Lungs e.g. diabetic ketones
Saliva/Sweat/Milk

Question 10

Fate of an orally administered drug

Where does the amount of drug available decrease

Answer 10

Oral - not dissolved
GIT - broken down in stomach/intestine/not absorbed
Liver - secreted into bile/metabolised
General circulation - plasma protein binding
In tissues - metabolised/excreted or tissue bound