Drug Receptor Interactions

Question 1

Differentiate between pharmacokinetics and pharmacodynamics

Answer 1

Pharmacokinetics - the effect of the body on the drug (e.g. absorption, distribution, metabolism, excretion) -

Pharmacodynamics - the effect of the drug on the body (responses produced, mechanism of action) (DD - Drug on body = pharmacoDynamics)

Question 2

List the types of drug target

Answer 2

Receptors

Ion Channels

Transport Systems

Enzymes

Question 3

Discuss receptor drug targets and give an example of a receptor target drug

Answer 3

• The terms agonist and antagonist refer to the receptor drug types
• four main families of receptors with different structures and transduction systems
• atropine is a muscarinic chonioceptor antagonist used to dry secretions

Question 4

List the two types of ion channels and give two common examples

Answer 4

1. Voltage sensitive (VGSC)
2. Receptor-linked (e.g. nAChR)

Examples:

1. Local anaesthetics - block VGSC
2. Calcium channel blockers - nifedipine, amlodipine

Question 5

Explain drugs that target transport systems, giving two examples of target systems and drug types targeting transport systems

Answer 5

Target carriers that transport susbstances against their concentration gradient. They are species specific.

Systems examples: Na+/K+ pump, NA uptake 1

Drug examples: Tricyclic antidepressants (TCAs) which interact with 5-HT transporters and NA transporters

Cardiac glycosides which increase contractility of the heart e.g. digoxin

Question 6

List the three ways that drugs interact with enzymes

Answer 6

1. Enzyme inhibitors - anticholinesterases - neostigmine
2. False substrates - methyldopa - antihypertensive
3. Prodrugs (PEF) - chloral hydrate - insomnia

Question 7

List two exceptions to the 4 target site rule

Answer 7

1. antacids which reduce stomach acidity
2. osmotic purgatives which draw water into the stomach contents and soften the stool

Question 8

Define potency

Answer 8

efficacy + affinity

Efficacy = ability of a drug to generate a response once it has bound to the receptor (usually involves a confirmational change)

Affinity = how willingly the drug binds to the receptor

Question 9

Draw a dose response curve for a full agonist in comparison to a partial agonist

Answer 9

Question 10

What happens if you administer a partial agonist and a full agonist together?

Answer 10

The effect is similar to an antagonist becuase the partial agonist interferes with the ability of the full agonist to generate a response.

Question 11

Draw a dose-response curve containing a full agonist, full agonist with lower affinity and a partial agonist.

Answer 11

Full agonists with lower affinity will still generate a maximal response but it will need a much higher concentration

The partial agonist curve will peak before it gets anywhere near the maximal tissue response

Question 12

Do anatagonists have affinity, efficacy or both?

What are the two main types of agonist?

Answer 12

Antagonists have AFFINITY but NO EFFICACY - bind and block to generate a response

There are TWO main types of antagonist:

1. Competitive

Examples: atropine - competitive muscarinic cholinoceptor antagonist, propanolol - competitive beta blocker (beta1 and beta2 adrenoceptor antagonist)

2. Irreversible

Example: hexamethonium - irreversible nicotinic cholinoceptor antagonist (it waits until the ion channel is open and then blocks the ion channel rather than just blocking a receptor)

Question 13

Draw a dose-response curve for an agonist alone, a competitive antagonist and an irreversible antagonist

Answer 13