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33 Cards in this Set

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Define Pharmacodynamics
Field of study that deals with the relationship between plasma concentration of a drug and the response obtained
Define affinity
Ability of a drug to bind to a receptor; on a graded dose-response curve, the nearer the curve is to the y axis, the greater the affinity (affinity deals with drugs acting on the same receptor)
Define efficacy
How well a drug produces a response; on a graded dose-response curve, the height of the curve represents the efficacy
Define potency
The amount of drug required to obtain a desired effect; on a graded dose-response curve, the nearer the curve is to the y axis, the greater the potency
Will the curves for two drugs acting on the same receptor be parallel or nonparallel to each other on a graded dose-response curve
Parallel
Will the curves for two drugs acting on different receptors be parallel or nonparallel to each other on a graded dose-response curve
Nonparallel
Define agonist
A drug that binds to a receptor, alters its conformation, and activates that receptor’s function
Define full agonist
An agonist capable of producing a maximal response
Define partial agonist
An agonist incapable of producing a maximal response; less efficacious than a full agonist
Define antagonist
A drug that binds to a receptor and prevents activation of a receptor
Define competitive antagonist
An antagonist that competes with an agonist for the same receptor site; graded dose-response curve will be shifted to the right (parallel) thus decreasing the agonist’s potency (and affinity); maximal response will not be affected
Define noncompetitive antagonist
An antagonist that acts at a different site from the agonist yet still prevents the agonist from activating its receptor; potency not affected; maximal response will be decreased; causes a nonparallel shift to the right on a graded dose-response curve
None
What happens when a partial agonist is added in the presence of a full agonist
The response of the full agonist is reduced; partial agonist is acting as an antagonist
How does a competitive antagonist affect Affinity (1/Km) of agonist
Decreased (thus Km will increase as it is inversely proportional to affinity)
How does a competitive antagonist affect maximal response (Vmax) of agonist
No change
How does a noncompetive antagonist affect the affinity (1/Km) of agonist
No change
How does a noncompetivie antagonist affect the maximal response (Vmax) of agonist
Decreased
Will increasing the dose of an agonist completely reverse the effect of a competitive antagonist
Yes
Will increasing the dose of an agonist completely reverse the effect of a noncompetitive antagonist
No
Define pharmacologic antagonism
Antagonist and agonist compete for the same receptor site
Define physiologic antagonism
Two different types of agonists acting at different receptors causing opposite responses, therefore, antagonizing each other (acetylcholine activating an M receptor to cause bradycardia is antagonized by norepinephrine acting at a beta receptor to cause tachycardia)
Define chemical antagonism
Response to a drug is antagonized by another compound that binds directly to the effector drug (digoxin is antagonized by Digibind which binds directly to digoxin and not its receptor)
Define potentiation
When one agonist enhances the action of another compound (benzodiazepines and barbiturates potentiate the effect of gamma-aminobutyric acid [GABA] on its receptor); graded dose-response curve is shifted to the left
What is a quantal (cumulative) dose-response curve
Curve showing the percentage of a population responding to a given drug effect vs. dose of drug given (or log of dose); allows you to visualize intersubjective variability regarding drug response in graph form
What is ED50
Estimation of the effective dose in 50% of a population; the dose at which 50% of the population will respond to the drug
Can you obtain the ED50 from a graded (quantitative) dose-response curve
No (this curve does not represent a population of individuals)
Can you obtain the ED50 from a quantal (cumulative) dose-response curve
Yes (this curve represents a population of individuals)
What is TD50
Estimation of the toxic dose in 50% of a population; the dose at which 50% of the population will have toxic effects from the drug
What is LD50
Estimation of the lethal dose in 50% of a population; the dose at which 50% of the population will die from the drug
What is therapeutic index (TI)
The relative safety of a drug by comparing the ED50 to either the TD50 or LD50; the safer the drug the “wider” the TI meaning the TD50 or LD50 is much greater than the ED50; drugs with a “narrow” TI have their TD50 or LD50 close to the ED50
How do you calculate TI
TI = TD50/ED50 or LD50/ED 50
What is a narrow therapeutic index (NTI)
Drugs with a NTI usually have a TI<2
List some examples of drugs with a NTI
Carbamazepine; digoxin; levothyroxine; lithium; phenytoin; theophylline; valproic acid; warfarin