3. Pharmadynamics

Question 1

What is pharmacodynamics?

Answer 1

What the drug does to the body.

Question 2

Name the 4 main types of Drug targets?

Answer 2

1. Receptors: Bind to the receptors (receive the drug) e.g. beta-blockers
2. Ion channels - drug molecules acts by blocking the ion channel (channel blocker) or by binding to but not blocking the channel (modulators) Eg. Calcium channel blockers
3. Carrier Molecules/ pumps  Eg. SSRIs
4. Enzymes - prevent release of enzyme
    Eg. Angiotensin converting enzyme (ACE) inhibitors

Question 3

Drugs acting on receptors can either be:

Answer 3

agonists or antagonists

Question 4

Difference between agonists and antagonists

Answer 4

Agonists = drugs that bind to receptor to produce a cellular response mimicking the action of endogenous ligands

Antagonist = drugs that bind to a receptor and prevent receptor activation by a natural ligand

Question 5

What happens when an agonist binds to a receptor?

Answer 5

• Agonists bind to receptor to activate them –> cellular response
• Agonists possess affinity and efficiency

Question 6

Define Affinity

Answer 6

= the ability of agonist to bind to a receptor

The higher the affinity, the slower the dissociation rate form receptor.
• Some drugs (antagonists) will bind to a receptor but will not activate it.

Question 7

Define Efficancy

Answer 7

= the ability of the drug to activate the receptor

Question 8

Define Potency

Answer 8

= the amount of drug needed for a response

• The higher the potency, the less drug is needed to get a response

Question 9

Define selectivity

Answer 9

•	Describes the ability of a drug to affect a particular target population e.g one receptor type
   o	Serotonin (5-HT) affects many different receptor types 
    o	Atenolol - B1 adrenoceptor selective (in heart) 
    o	Salbutamol - B2 
 Adrenoceptor selective (in the lungs)

• No drug is 100% selective in its action, In many cases increasing the dose of a dug will cause it to affect targets other than the principle one and this can lead to side effects

Question 10

Define antagonist

Answer 10

• Bind to receptors but do not activate them - no cell response
• Antagonists block receptor activation by agonists - no cell response
• Antagonists possess affinity but lack efficacy

Question 11

What is competitive antagonism

Answer 11

• Binding of agonist and antagonist occur at the same (orthostatic) site and is this competitive and mutually exclusive (naloxone and morphine)

Question 12

What is non competitive antagonism

Answer 12

• Antagonists bind to an allosteric site to prevent activation of the receptor
• Both agonist antagonists may occupy the receptor simultaneously but activation cannot occur when antagonist is bound

Question 13

What is Adverse Drug event?

Answer 13

• An injury resulting from medical intervention relating to a drug
• Occurs while a person is taking the medication but not necessarily due to the drug
• Incudes medication errors and adverse drug reactions

• Examples
o Aspiration pneumonia resulting from drug overdose

Question 14

What is an adverse drug reaction?

What are the types

Answer 14

Any response to a drug which is:
• Noxious (harmful)
• Unintended (but expected - side effects)
• Occurs at doses normally and appropriately used ini humans for prevention, diagnosis or treatment of a disease

Type A - pharmacological effects that are Predictable and dose dependent
• Side effect, toxicity, drug interactions

Type B - Hypersensitivity reactions that are unpredictable and not dose dependent (idiosyncratic)

Question 15

Three types of ADRs

Answer 15

1. Allergy (unpredictable) = adverse effects involving immunological system
   e. g. penicillin anaphylaxis
2. Side effect (predictable) = any. unintended effect, occurring at doses normally used
3. Drug Interaction (predictable) = interaction with another medicine causing a variation in pharmacological effect

Question 16

Types of drug interactions

Answer 16

Psychiochemical

pharmacokinetic dug interaction

pharmacodynamic interactions

Question 17

Psychiochemical drug interactions

Answer 17

Physical incompatibility
Implications
• drugs may not be compatible in intravenous mixtures reduced solubility may prevent absorption
• drugs may interact with inert excipients within a dose form
• may de-stabilise dose forms –
• may render drug and dose form ineffective or possibly dangerous (e.g. particulate matter)

Question 18

Pharmacokinetic drug interactions

Answer 18

•	Absorption 
o	Normally food interactions 
•	Distribution 
o	Including protein binding 
•	Metabolism
o	Cytochrome P450 
•	Renal elimination 
o	Competition for active efflux/ tubular Reabsorption

Question 19

Pharmacodynamic interactions

Answer 19

Drugs with
• Similar mechanism of action
• Similar pharmacological effects
• Antagonistic (reduced effectiveness; risk of lock of effect
o E.g. morphine and naloxone
• Agonistic (increase effectiveness: risk of toxicity)
o E.g. benzodiazepine and alcohol