Pharmacodynamics Flashcards
What does Pharmacodynamics study?
Pharmacodynamics studies the mechanism of the physiological effect of a drug and the varying magnitude.
If drug A has a higher Emax than drug B, what is implied?
Emax (Efficacy) is considered the maximum effect produced by the agonist.
A higher Emax implies drug A is more Efficacious than Drug B.
That is, it has a higher ability to produce the desired or intended result.
If Drug A has a higher ED50 than Drug B, what is implied?
ED50 (Potency) is the concentration of drug which produces 50% of Emax, thus it is a measure of Potency.
A higher ED50 implies that drug A is more Potent than drug B.
How do potency & efficacy relate?
Potency (EC50) & efficacy (Emax) are independent of eachother. Neither can predict eachother.
Efficacy is usually more important in therapeutics
What does higher potency imply in therapeutics?
Higher potency can indicate greater selectivity and thus fewer side effects.
Why not always use a dose much larger than the EC50 to insure max therapeutic effect?
Increasing the dose/concentration may cause adverse side effects.
In general, increasing the dose closer to the Emax increases the chance of developing adverse side effects.
Give the equation for the Dose-Response Curve
Dose-Response Curve:
Describe how the effect equation can be used to calculate an effect, given a certain concentration.
How do Potency (Emax) & Efficacy (ED50) relate?
Potency (EC50) & efficacy (Emax) are independent of eachother. Neither can predict eachother.
Efficacy is usually more important in therapeutics.
What is the purpose of Quantal Response curves?
What are the variables measured?
Quantal Response Curves are used to determine the safety of a drug.
ED measures the Efficacy
LD measures the Lethality, with LD50 indicating the dose at with 50% of the subjects die.
What quantities can be determined from Q-R curves?
Therapeutic Index (TI): The distance between ED50 & LD50
Margin of Safety (MofS): Distance between ED99 & LD1
If a Margin of Safety is <1, what may occur if you push to achieve maximum effect?
If you push to achieve maximum effect, you’ll begin killing people
Agonist Only: Curve 2
Agonist + Competitive Inhibitor (antagonist): ?
Agonist Only: Curve 2
Agonist + Competitive Inhibitor (antagonist): Curve 3
Explain Curve 1
Curve 1 indicates a partial agonist given in the presence of a full agonist.
“At high [Partial Agonist], the response drops to the efficacy of the partial agonist as it displaces the full agonist from the receptor. A high dose of a partial agonist can lower the response to a full agonist.”
Explain the 2 potential causes of Curve 4.
- Partial Agonist
- Agonist + irreversible antagonist (inhibitor) compared to Curve 2
What is curve 5?
Curve 5 is an inverse agonist
For most drugs, how does EC50 compare to KD?
Why?
For most drugs EC50 < KD
This is because of the presence of spare receptors, which functions to;
- Increases the sensitivity of a cell to an agonist
- Facilitate repeated responses to an agonist & resist desensitization
In a cell with spare receptors, how does the Binding curve compare to the Response curve?
Given (3) cells with different quanities of receptors to an agonist, describe how the D-R curve would result.
A: No Spare R.
B: 1x Spare R.
C: 10x Spare R.
Spare receptors reduce EC50 and thus increase potency
Comparing Partial to Full Agonists, what differs?
Partial Agonists have lower efficacy than Full agonists (lower Emax)
Potency can vary, independent of the full agonist
If a Full agonist is present and a partial agonist is administered, what occurs?
What is the R-> R* model?
Adding a competitive antagonist to an Agonist causes what type of shift to the DR curve?
A parallel right shift with no effect on Emax.
Adding an irreversible inhibitor to an Agonist causes what type of change on the DR curve?
