Pharmacodynamics & kinetics Flashcards
Definition of affinity
The tendency of a ligand to bind to a receptor
Definition of efficacy
The ability of a ligand to produce a biological response.
What is Intrinsic efficacy?
The ability of a ligand to generate the active form of the receptor.
What is an agonist?
Ligand that creates a response in the receptor
What is an antagonist?
Ligand that binds to the receptor but doesn’t create a response.
What is Bmax?
The maximum binding capacity.
What is Kd?
Concentration of ligand required to occupy 50% of available receptors.
How does Kd relate to affinity?
The lower the Kd the higher the affinity.
What is Emax?
The maximum response that can be measured.
What is EC50?
Concentration of agonist required to produce half of the maximal response
Definition of agonist potency
The concentration of a drug that creates 50% of it’s maximal response.
The lower the value of EC50 the more potent the drug.
What is a partial agonist?
An agonist that produces a response that is lower than that produced by a full agonist.
What is reversible competitive antagonism?
The antagonist binds to the orthosteric site (competitive).
It binds with weak (non-covalent bonds) hence reversibility.
What is Irreversible competitive antagonism?
Antagonist binds to orthosteric site.
With strong bonds which are hard to break. (Possibly covalent bonds)
What is non-competitive antagonism?
Binding occurs on the allosteric site.
Interaction could be either low or high affinity.
What does a Kd greater than EC50 indicate?
That there are spare receptors
What is bioavailability?
The fraction of a dose that reaches the target body compartment.
What factors affect drug absorption?
GI Length
Blood flow in GI
Food pH (low pH can destroy some drugs)
First pass metabolism by GI and liver (drug is broken down)
How do you calculate bioavailability?
Amount reaching systemic circulation / Total drug given IV
This works because in IV 100% of the drug reaches the target.
What is volume of distribution (Vd)?
A measure of how well a drug penetrates into interstitial and intracellular compartments.
How do you calculate Vd?
Drug Dose / Concentration of drug in plasma.
