Principles of Pharmacodynamics

Question 1

What is a drug?

Answer 1

a chemical that interacts with the body and causes a specific physiological response

Question 2

What is a drug target site?

Answer 2

cellular macromolecule that will bind a certain drug

Question 3

What is a receptor?

Answer 3

drug recognition site, when unbound it is unfunctional/functionally silent

Question 4

What is an agonist?

Answer 4

binds to a receptor and activates it

Question 5

What is an antagonist?

Answer 5

binds to receptor but has no activation

Question 6

What is affinity?

Answer 6

How avidly a drug binds to its receptor

Question 7

What is efficacy?

Answer 7

The ability of a drug to cause a conformational change within the receptor in order to have its physiological effects

Question 8

What is potency?

Answer 8

measure of drug strength

Question 9

What is selectivity?

Answer 9

only binding to a particular subset of receptors, usually requires low dosage

Question 10

What is a partial agonist?

Answer 10

less efficacy and affinity, cannot cause max tissue response

Question 11

What are the principle differences between competitive and irreversible antagonists?

Answer 11

competitive = propranolol
irreversible = hexamethonium --> increasing level of agonist has no effect on tissue response

Question 12

Describe the four main categories of drug target sites and give one example of a drug acting at each of these different target sites

Answer 12

RITE
Receptors –> beta receptor agonists eg. adrenaline
Ion channels –> voltage sensitive calcium channels eg. nifedipine
Transport systems –> uptake mechs eg. Na/K+ - digoxin
Enzymes –> anticholinesterases eg. neostigmine or phygostigmine

Question 13

Specify two classes of drugs that do not act by binding to proteinaceous target sites

Answer 13

antacids –> chemical reaction

diuretics –> ion channels

Question 14

Define ‘receptor reserve’. What is the importance of this physiological pheonomenon?

Answer 14

repeated activation will exhaust mediator stores –> all receptors endocytosed
maximal response can be achieved without occupying all the receptors

Question 15

What is the structure activity relationship?

Answer 15

The structure–activity relationship (SAR) is the relationship between the chemical or 3D structure of a molecule and its biological activity.

Question 16

Differentiate between the four principal types of drug antagonism. Give one example of each type of agonist.

Answer 16

receptor blockade
homeostatic/physiological antagonism - Na+A and H2 - decrease in TPR
chemical - dimercaprol - chelates lead
pharmacokinetics - upregulates liver enzymes eg. Warfarin

Question 17

Name four main receptor families

Answer 17

Ion channel
G-protein
TK
intracellular/DNA/nuclear eg. steroids

Question 18

List five cellular mechanisms that may account for drug tolerance

Answer 18

exhaustion of mediator stores
receptor endocytosis
increased metabolism
change in receptors
physiological

Question 19

Which way do competitive antagonists shift the log dose-response curve?

Answer 19

RIGHT

same maximal response achieved

Question 20

Which way do reversible antagonists shift the log dose-response curve?

Answer 20

LEFT

at high dose, maximal response is impaired