Pharmacodynamics

Question 1

Selectivity

Answer 1

Different receptors may have different drug affinities.

Drug fits in one receptor at one site better than other receptors at different sites.

Question 2

Receptor subtypes
(often one drug will act at one receptor subtype but not another)

Answer 2

Different receptors that respond to the same natural substance.
*Example: Norepinephrine acts at five subtypes of receptors.

Question 3

Examples of selectivity:

Answer 3

1. Non-selective:
   Beta blocker Propanolol blocks both Beta 1 and 2 receptors.
   Beta-one being blocked=reduced BP.
   Beta-2 receptors are those that open bronchioles, not good for asthmatics.
2. Selective drug: Atenolol, selectively blocks beta-1’s
   **Some anti-histamines block other receptors (cholinergic, adrenergic)–>sleepy and non-allergic after taking them

Question 4

Non-selective drugs: most drugs are like this

Answer 4

In this case, 90% of receptors A are occupied at the same time that 75% of receptor B’s are occupied.

Question 5

Rules of selectivity

Answer 5

1. The more selective, the better (some are more selective than others).
2. Even most “selective” drugs can become nonselective at higher concentrations. (start activating other receptors that may or may not be related).

Question 6

Drug toxicity definitions of TD50 and LD50 (quantal responses)

**[Drug] or [D]= concentration

Answer 6

TD50: [D] in blood that causes 50% of ppl to have a toxic reaction.

LD50: dose where 50% of subjects die.

Question 7

Drug toxicity definitions of TD90 and LD90

Answer 7

TD90: [D] in blood that causes 90% of ppl to have toxic reaction.

LD90: where 90% of subjects die.

Question 8

Therapeutic index is defined as:

Answer 8

LD50/ED50, not best measure of safety

If LD50=10uM and ED50=0.5uM
TI=20

Question 9

Protective index

Answer 9

TD50/ED50

Question 10

Margin of safety:

Answer 10

LD1/ED99

Question 11

Therapeutic window:

Answer 11

In a graph, is the area between the Therapeutic effect curve and the Toxic effect curve.