Lecture 02 - Principles of Pharmacology

Question 1

What is the definition of a drug?

Answer 1

1. Substance that interacts with a biological system and changes it.

Question 2

What three types of name does a drug have and how are they used?

Answer 2

1. Chemical name - not generally used e.g. acetylsalicyclic acid
2. Generic name - commonly used e.g. aspirin
3. Trade name - by doctors and marketing e.g. Aspro

Question 3

There are six types of drugs that have their effect due to their physio chemical properties.

What kind of effect do they have?

What are they, and how do they work?

Answer 3

1. Required in high concentration with non-specific effects.
2. Antacid - base, increases pH, counters indigestion
3. Bulk laxative - not absorbed, stretches gut walk, relieves constipation
4. Osmotic laxative - increases amount of water in faeces
5. Osmotic diuretics - given by IV, filtered in kidneys, not reabsorbed in bloodstream leading to more urine
6. General anaesthetic - lipid soluble so interacts with lipids in cell membrane, makes individual unconscious
7. Alcohol - acts as a general anaesthetic

Question 4

What is the definition of potency?

Answer 4

1. The measure of drug activity in a biological system.

2. Most drugs are effective at a low concentration.

Question 5

What is the definition of affinity?

Answer 5

1. The strength of the drug receptor interaction.

2. A potent drug has high affinity.

Question 6

In what two ways are drugs specific?

Answer 6

1. Chemical specificity

2. Biological specificity

Question 7

How does chemical specificity work?

Answer 7

1. Drugs are specific and complimentary to their receptor.
2. Lock and key model.
3. Allows for altering of cell function.

Question 8

How does biological specificity work?

Answer 8

1. Molecule and receptor are the same.
2. But receptors are located on different tissues.
3. Will lead to different effects.
4. e.g. Ach makes the heart slow down, but makes the gut contract

Question 9

What does competition affect?

Answer 9

1. The efficacy of drugs, as receptors are competed for.

Question 10

How does one prepare an isolated ileum?

Answer 10

1. Ach causes contraction
2. Ach washes out to allow relaxation
3. Histamine contracts
4. Histamine washed out to allow relaxation
5. Atropine added, and always present
6. Ach added, but no effect due to competition
7. Histamine added, contraction as His has its own receptor
8. Atropine blocks only Ach receptors, not His, hence chemically specific
9. A higher dose of Ach leads to contraction as it then competes better

Question 11

What is an agonist?

Answer 11

1. They bind to a receptor and produce a response.
2. Have both affinity and efficacy (since they can produce a change in cells).
3. E.g. Ach and His

Question 12

What is an antagonist?

Answer 12

1. Bind to the receptor but do not produce a response.
2. Prevent the binding of the agonist.
3. Hence blocks or reduces the response to an agonist.
4. Possess affinity but not efficacy.

Question 13

What are the three types of antagonists?

Answer 13

1. Competitive
2. Irreversible
3. Other

Question 14

What is the relationship between drug concentration and response?

Answer 14

1. Graded - level of increase of the response changes as concentration changes.
2. Saturating - maximum response can not be exceeded.
3. Exhibits threshold - minimum concentration required for effect.

Question 15

What are the characteristics of the drug concentration-response graph?

Answer 15

1. Drawn as log graph to clearly show the effect of low doses.
2. E (max) describes the concentration which produces the maximal response.
3. E (50) is concentration which produces 50% of the maximum response - commonly used as a convenient point to examine.

Question 16

What is the law of mass action?

Answer 16

1. The rate of chemical reaction is directly proportional to the masses of the reactant concentrations.
2. Therefore p (occupancy) = number of drug-receptor complexes formed divided by total number of receptors present.