Session 9 - Pharmacodynamics

Question 1

What is pharmacodynamics?

Answer 1

The biochemical, physiologic and molecular effects of drugs on the body and involves receptor binding, post-receptor effects and chemical interactions

Question 2

What is Kd and how is it used?

Answer 2

Kd = dissociation

- It is the concentration at which 50% of all available receptors are bound used as a measure of affinity

Question 3

With respect to affinity and efficacy define an agonist and an antagonist

Answer 3

Agonist - have affinity and efficacy - i.e. they have affinity and bind to a receptor as well as having intrinsic efficacy whereby they can stabilise/generate an active form of the receptor
Antagonist - These drugs bind to the receptor and simply block the binding. They do not cause the receptor to have any conformational change

Question 4

What is the difference between clinical efficacy and pharmacological efficacy?

Answer 4

• Pharmacological efficacy simply looks at the drugs ability to generate an active form of the receptor. Whereas clinical efficacy looks at it’s physiological effects such as whether it lowers blood pressure. This can be effected by it’s metabolism and absorption.

Question 5

Using morphine, naloxone and fentanyl as an example, explain the effects of affinity to drugs

Answer 5

• Morphine or heroin (agonists of mu - opioid receptors) if taken as an overdose, can lead to respiratory depression and as such death.
• Naloxone - a higher affinity antagonist will outcompete morphine or heroine reducing its effects.
• Fentanyl however has an even higher affinity as an agonist and as such naloxone is ineffective.

Question 6

What is potency and what is used to represent it?

Answer 6

• Potency is a measure of a drugs ability to generate a physiological response
• It is measured as EC50: the concentration required to generate 50% of the maximum response

Question 7

What is strictly meant by “concentration” and “dose”?

Answer 7

Concentration - the known concentration of drug at the site of action - e.g. in cells and tissues
Dose - the dose (quantity) given to a patient at the point of administration