mechanisms of drug action

Question 1

Define pharmacodynamics.

Answer 1

Effect of drug on body relating to mechanism of action.

Question 2

Give 4 examples of drug target sites.

Answer 2

1. Receptors,
2. Ion channels,
3. Transport systems,
4. Enzymes.

(proteins)

Question 3

What are receptors?

What activates them?

What do agonists and antagonists do + examples.

How many types of receptors?

Answer 3

Proteins within cell membranes (normally)

Activated by NT or hormone.

Agonist stimulate, antagonist inhibit. ACh = agonist, atropine = antagonist

4 types

Question 4

What are ion channels?

Outline 2 types.

2 examples of drugs that act on ion channels.

Answer 4

Selective pores - allow ion transfer down electrochemical gradient.

1. voltage sensitive (e.g. VSCC).
2. receptor-linked (e.g. nAChR)
   e. g. local anasthetics and Calcium channel blockers.

Question 5

What is a transport system.

What do they transport (examples)

Drug examples.

Answer 5

Transport substances against their concentration gradient.

Specific for certain species.

e.g. Na+/K+ ATPase antiporter.

drug examples: tricyclic anti-depressants (TCAs), cardiac glycosides.

Question 6

What are enzymes?

Outline 3 ways drugs interact with enzymes + examples.

Answer 6

Catalytic proteins - increase rate of reactions

Drug interactions -

1) enzyme inhibitors
e. g. anticholinesterases (neostigmine)
2) false substrates
e. g. methyldopa
3) prodrugs
e. g. chloral hydrate ® trichloroethanol

Can have unwanted effects. e.g. paracetamol.

Question 7

How else might drugs bring about their effect?

Answer 7

physiochemical properties

e.g. antacids (basic substances that reduce stomach pain since they’re basic)

osmotic purgatives (draw H2O into gut - softening stools + aiding passing. work because of aformentioned physiochemical properties.

Question 8

How can reservoirs of inactive drugs form?

Answer 8

Plasma protein binding (PPB)

Question 9

How do antagonists inhibit function?

Answer 9

Blocking action of agonist. Bind + do nothing

Question 10

What determines drug potency?

Answer 10

Affinity - ability to bind

Efficacy (‘intrinsic activity’) - action once bound (e.g. conformational change in receptor)

Question 11

What’s the difference between a full and partial agonist?

How can a partial agonist act as an antagonist?

Answer 11

A full agonist can illicit a full response, partial agonists can never generate 100% of a response.

In the presence of a full agonist.

Question 12

Define selectivity.

Answer 12

Degree of preference of drug for target receptor: overlap onto different receptors (especially at higher conc.)

Question 13

Explain the structure-activity relationship.

Answer 13

The structure of a drug is directly related to its activity.

Small changes in drug structure can effect efficacy/affinity and its pharmokinetics.

Question 14

Draw a dose-response curve comparing full and partial agonists.

+ the logarythmic equivalent.

Answer 14

Question 15

Outline antagonist affinity and efficacy.

Answer 15

high affinity, no efficacy.

Question 16

What are the 2 types of receptor antagonist?
+ examples

Answer 16

1. competitve: same site as agonist, surmountable, shift D-R curve to right
   e. g. atropine, propranolol
2. irreversible: bind tightly/at different site, insurmountable.
   e. g. hexamethonium.

Question 17

Draw a logarythmic curve comparing tissue response against log[Agonist] including competitve/irreversible antagonist.

Answer 17