2: Drug movement in the body

Question 1

What are the four processes making up the fates of drugs in the body?

Answer 1

Absorption

Distribution

Metabolism

Excretion

Question 2

What is absorption?

Answer 2

Process by which drugs enter the body from their site of administration

Question 3

What is distribution?

Answer 3

Movement of drug from site of administration, through the bloodstream, and into the tissues

Question 4

What is metabolism of a drug?

Answer 4

Conversion of active drug to a less active form by enzymes

Question 5

Where does drug metabolism usually occur?

Answer 5

Liver

Question 6

What is excretion of a drug?

Answer 6

Removal of drug from the body

Question 7

Where does drug excretion usually occur?

Answer 7

Kidneys

Question 8

In which two organs are ingested drugs absorbed?

Answer 8

Stomach

Small intestine

Question 9

By which circulation do ingested drugs reach the liver?

Answer 9

Portal circulation

Question 10

Where do drugs go once they have been metabolised in the liver?

Answer 10

Kidneys for excretion

usually

Question 11

Drugs with (high / low) lipid solubility will be absorbed more quickly.

Answer 11

high

Question 12

Drugs with (high / low) lipid solubility will be absorbed slowly.

Answer 12

low

Question 13

Can ions move easily across the phospholipid bilayer?

Answer 13

No

Question 14

An acid (donates / accepts) protons.

A base (donates / accepts) protons.

Answer 14

Acids are proton donators

Bases are proton acceptors

Question 15

Only the (ionic / unionised) forms of drugs move easily across the phospholipid bilayer.

Answer 15

unionised

Question 16

How is pH calculated?

Answer 16

pH = -log₁₀[H⁺]

Question 17

What is pK_a?

Answer 17

Acid dissociation constant

i.e pH at which drug is 50/50 ionised/unionised

Question 18

Acidic drugs become (more / less) ionised in an acidic environment.

How does this affect their lipid solubility?

Answer 18

less

Greater absorption due to increased lipid solubility (unionised)

Question 19

Basic drugs become (more / less) ionised in a basic environment.

What effect does this have on their lipid solubility.

Answer 19

less

Greater absorption due to increased lipid solubility (unionised)

Question 20

Where does the overwhelming majority of absorption occur?

Answer 20

Small intestine

Question 21

What is motility?

Answer 21

Rate of stomach emptying and food movement through the intestines

Question 22

Apart from drugs, what affects gastrointestinal motility?

Answer 22

Presence of food in the GI tract (see satiation signals)

Question 23

In the presence of food, gastrointestinal blood flow (increases / decreases).

What cardiovascular condition can this cause?

Answer 23

increases

Angina

Question 24

What is oral availability?

Answer 24

The amount of drug which reaches the systemic circulation after oral ingestion

or

amount in system circulation / amount ingested

Question 25

What is **systemic availability**?

Answer 25

The fraction of drug which **reaches the systemic circulation** after **absorption** or amount in system circulation / amount absorbed

Question 26

What is the **systemic availability (%)** of IV drugs?

Answer 26

**100%**

Question 27

What is **oral** administration?

Answer 27

**Ingestion by mouth**

Question 28

What is **sublingual** administration?

Answer 28

**Drug held under the tongue**

Question 29

What is **buccal** administration?

Answer 29

**Drug held against the inside cheek**

Question 30

What is **rectal** administration?

Answer 30

**Drug inserted via the rectum**

Question 31

What is **intravenous** administration?

Answer 31

**Drug administered via veins**

Question 32

What is **intramuscular** administration?

Answer 32

**Drug injected directly into muscle**

Question 33

What is **subcutaneous** administration?

Answer 33

**Drug administered under the skin**

Question 34

What is **inhalational** administration?

Answer 34

**Drug is breathed in** (e.g nebulised salbutamol)

Question 35

What is **transdermal** administration?

Answer 35

**Drug is applied to skin** (e.g patches)

Question 36

What is **topical** administration?

Answer 36

**Drug is applied to specific skin surfaces / mucous membranes**

Question 37

Only **(ionised / unionised)** drugs move readily by diffusion.

Answer 37

**unionised** because cell membranes are impermeable to ions.

Question 38

What is **volume of distribution** (V_d)? What is the unit?

Answer 38

**Amount of drug in body / Plasma concentration** **Litres (L)**