Pharmokinetics

Question 1

A drug is…

Answer 1

A single chemical entity that may be one of the constituents of a medicine

Question 2

A medicine…

Answer 2

May include one or more active drugs together with additives that facilitate administration

Question 3

An excipient is…

Answer 3

The ‘vehicle’ via which a drug can be administered

Question 4

Therapeutic index is…

Answer 4

The margin between an effective dose of a medication, and a dose that will cause harm

Question 5

2 types of administration route

Answer 5

Enteral - via gut, oral or rectal

Parenteral - avoiding gut, on skin, under tongue, via lungs

Question 6

Absorption

Answer 6

Lipid-soluble drugs can dissolve through membranes

Question 7

What are the GI factors influencing absorption? (4)

Answer 7

Oesophageal passage
Gastric motility (peristalsis)
Presence of food and drink (200ml water is ideal)
pH

Question 8

How does pH affect absorption?

Answer 8

Lots of drugs are made basic so they’re water-soluble in the stomach, then carried in solute to the intestine where acidity reduces and the drug becomes fat-soluble

Question 9

The small intestine is the largest area of absorption because…

Answer 9

It has a large surface area

Question 10

Drug efflux proteins…

Answer 10

Sit in the cell membrane and reject drugs trying to pass through, and vacuum drugs that have entered the cell and reject them

Question 11

Drug efflux proteins… over time because… which explains…

Answer 11

Increase
The body makes more and more
Why drug resistance builds up

Question 12

Distribution is…

Answer 12

The amount of drug in body tissues, fluids or spaces. The movement of a drug between the blood plasma and tissues continues until the drug equilibrates.

Question 13

The more fat-soluble the drug…

Answer 13

The faster it will leave the bloodstream - leaves and stores in fat

Question 14

…affects blood flow in the tissue

Answer 14

Heat

Question 15

Plasma protein binding

Answer 15

The more fat-soluble a drug is, the more it will bind to proteins. Drugs compete for protein-binding sites.

Question 16

Metabolism

Answer 16

Enzymes metabolise drugs to make them water-soluble, so they stay in the bloodstream and are filtered out by liver rather than going to target cells

Question 17

Phase I metabolism

Answer 17

Drug is broken up into metabolites by enzymes (women have half of these enzymes compared to men)

Question 18

Phase II metabolism

Answer 18

Metabolites (or original drug) are conjoined with another molecule, making it more water-soluble

Question 19

… are phase 1 metabolic enzymes

Answer 19

Cytochrome P450

Question 20

… is the enzyme respondible for metabolising >60% of all therapeutic drugs

Answer 20

Cyp 3A4

Question 21

… is an enzyme responsible for metabolising most antidepressants

Answer 21

Cyp 2D6

Question 22

First pass effect

Answer 22

The extent of metabolism experienced by a drug after it passes through the liver/intestine wall.
If a drug has a high first pass effect, there is not much of the drug left in the bloodstream for effect - parenteral routes avoid this

Question 23

… is an example of a drug that is effective after it is metabolised

Answer 23

Morphine

Question 24

3 methods of eliminating drugs from plasma

Answer 24

1. Redistribution
2. Liver metabolism
3. Renal excretion

Question 25

Half life

Answer 25

How long it takes to clear 50% of a drug in a person’s body