Lecture 2: Drug disposition

Question 1

What are the 4 processes that happen to drugs in the body?

Answer 1

Absorption

Distribution

Metabolism

Excretion

Question 2

Describe absorption of a drug and where it occurs.

Answer 2

The process by which a drug enter the body (Note the lumen of the GI tract is outside the body) from the site of administration, mostly occurs in small intestine.

Question 3

Describe distribution of a drug. (2)

Answer 3

• The process by which a drug leaves the circulation and enters the tissues perfused by blood.
• Once inside the tissue further distribution may occur by diffusion or carrier mediated transport

Question 4

Describe metabolism of a drug, and where it mainly occurs.

Answer 4

The process in which tissue enzymes catalyse the chemical conversion of a drug to a more polar form that is more readily excreted from the body. (Primarily in the liver by hepatic metabolism)

Question 5

Describe excretion of a drug, and where this mainly occurs.

Answer 5

The processes that remove a drug from the body (Principally in the kidneys by renal excretion)

Question 6

Name and describe the four factors that affect drug absorption.

Answer 6

• Solubility- The drug must dissolve to be absorbed
• Chemical stability- Some drugs are destroyed by acid in the stomach or enzymes in the GI tract- so drugs must be stable in acid and resistant to enzymes
• Lipid to water partition coefficient- The ratio of how much a drug likes to be dissolved in lipid compared to water.
• Degree of ionisation- Many drugs exist as weak acids or bases.

Question 7

What is the Henderson-Hasselbalch equation?

Answer 7

An equation used to calculate the proportion of ionised and unionised drugs.

Question 8

Name enteral routes of drug administration. (3)

Answer 8

Oral (By mouth)

Sublingual (Under the tongue)

Rectal (Via the rectum)

Question 9

Name parenteral routes of drug administration.

Answer 9

Intravenous (into a vein)

Intramuscular (into a muscle)

Subcutaneous (injected into the skin)

Inhalational (Through the nasal cavity)

Topical (applied to body surface)

Question 10

Name the two forms that drugs can exist within compartments in.

Answer 10

Bound and free

Question 11

Which form of drug can move between compartments?

Answer 11

Free form

Question 12

What is the Volume of distribution? (Vd)

Answer 12

The apparent volume in which a drug is dissolved.