2.2 Pharmacodynamics

Question 1

What is pharmacodynamics?

Answer 1

The study of the effect of drugs and their mechanisms of action on the body

Question 2

Where do drugs work?

Answer 2

• cell surface receptors
• nuclear receptors
• enzyme inhibitors
• ion channel blockers
• transport inhibitors

Question 3

What is the importance of drug selectivity?

Answer 3

The more selective a drug is for its target, the less chance that it will interact with different targets and have less undesirable side effects.

Target them against a specific receptor subtype to be targeted against specific organ
E.g heart b1
Lungs b2

Question 4

How can high doses of salbutamol effect vasoculture?

Answer 4

Tachycardia

B2 receptors in lungs, also in blood vessels causes vasodilation = fall in TPR = tachycardia

Question 5

What is affinity?

Answer 5

Defines the tendency of a drug to bind to a specific receptor type

Question 6

What is efficacy?

Answer 6

The ability of a drug to produce a response as a result of the receptor or receptors being occupied

Described the max effect of a drug

Question 7

What is potency?

Answer 7

Dose required to produce the desired biological response. Describes the different doses of two drugs required to the exact the same effect.

Question 8

What is the therapeutic index?

Answer 8

The relationship between concentrations causing adverse effects and concentrations causing desirable effects.
Ideally want a wide index

Index = EC50 (adverse effect)/ EC50 (desired effect)

Question 9

What is the therapeutic window?

Answer 9

The range of dosages that can effectively treat a condition while still remaining safe. It is the range between the lowest dose that has a positive effect and the highest dose before the negative effects outweigh the positive effects.

Question 10

What agonist and antagonists work at the same receptor?

Answer 10

Opiated
Naloxone
Beta blockers
B2 agonists

Question 11

What agonist and antagonists work at different receptors?

Answer 11

Warfarin and aspirin are examples

Question 12

What are examples of non selective drugs?

Answer 12

Anti depressants work on manny receptor subtypes e.g adrenergic and noradrenergic

Question 13

Name drugs that are cleared renally?

Answer 13

Digoxin, aminoglycoside antibiotics

Question 14

What happens in hepatic disease?

Answer 14

Reduced clearance of hepatic metabolised drugs
Reduced CYP 450 activity
Much longer half lives
Toxicity 
Classic = opiates in cirrhosis

Question 15

What does falling cardiac output lead to?

Answer 15

Excessive response to hypotension agents

Reduced organ perfusion

• reduced hepatic blood flow and clearance
• reduced renal blood flow and clearance

Question 16

What is an adverse drug reaction?

Answer 16

An unwanted or harmful reaction which occurs after administration of a drug or drugs and is suspected or known to be due to the drugs

Question 17

What puts people at high risk for adverse reactions?

Answer 17

• polypharmacy
• patient at extremes of age = altered pharmacokinetics profiles (renal/hepatic) or co morbidities
• reckless prescribing
• multiple medical problems
• use of drugs with narrow therapeutic indexes = high risk of toxicity
• drugs are being used near their minimum effective concentration = increased risk of treatment failure if metabolism increased

Question 18

Why are there variabilities in drug responses with people?

Answer 18

Body weight and size
Age and sex
Genetics
Condition of health 
Placebo effect

Also due to conditions of administration

• dose and route
• drug resistance
• drug interactions e.g chemical or physical, GI absorption, metabolism, excretion, etc.

Question 19

What is a loading dose?

Answer 19

A loading dose is an initial higher dose of a drug that may be given at the beginning of a course of treatment before dropping down to a lower maintenance dose.

A loading dose is most useful for drugs that are eliminated from the body relatively slowly, i.e. have a long systemic half-life