9 pharmacodynamics II Ngu

Question 1

Apply your knowledge of relative potency and (maximum) efficacy to select the best drugs (from many choices) with which to treat a patient with a given disease.

Answer 1

efficacy is a measure of a drugs ability to bring about a desired effect and should be the first thing that is selected for when looking for a drug

potency is the measure of what dose is necessary to bring about an effect

potency should be balanced to bring about just the right effect while minimizing toxicity by choosing the drug with the right efficacy as well as using a drug that is potent enough to be effective easily but not so that it is too easy to reach toxic doses

Question 2

Use your understanding of the factors influencing (drugs’) efficacy to optimize therapy in patients with regards to size, age, gender, metabolism

Answer 2

size –> larger = higher Vd which is inv. proportional to efficacy

age –> older = lower Vd = higher efficacy at lower doses

gender –> men = higher Vd = lower efficacy at given dose vs women

metabolism –> lower metabolism will mean drug effects last longer –> longer intervals/half life

Question 3

Apply your knowledge of graded dose response curve to identify drugs with higher propensities to cause harm in patients.

Answer 3

when comparing response(Y) to dose(x) graphs, potency increases as a curve moves to the left and becomes more dangerous as the response curve is more steep which indicates a narrow range of effect = increased risk of toxicity

Question 4

Apply your knowledge of the quantal dose response curves to ID the following:

ED50

TD50

LD50

therapeutic index

Answer 4

ED50–> dose where 50% of subjects demonstrate beneficial effects

TD50–> dose where 50% of subjects demonstrate harmful effects

LD50–> dose where 50% of subjects are dead due to the drug

therapeutic index = TD50/ED50 = margin of safety

Question 5

Define the following variations of drug responses that can occur during drug therapy

Idiosyncratic
Hyporeactive
Hyperreactive
Tolerance
Tachyphylaxis

Answer 5

Idiosyncratic –> unusual adverse response independent to dose and allergy ie. angioedema

Hyporeactive–> drug does not elicit the same efficacy as expected

Hyperreactive–> drug elicits efficacy sooner than expected

Tolerance–> receptor is internalized on overstimulation ie. Nitroglycerin for angina

Tachyphylaxis–> receptor is simply inhibited from binding via beta arrestin ie. scopolamine for coast guards