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Pharmacodynamics
Lecture 7: Pharmacodynamics
28
Pharmacology
Graduate
06/23/2010

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Term
What is the fundamental principle of pharmacodynamics?
Definition
Drugs can only modify underlying biochemical or physiological process.

drugs can NOT "create" effects.
Term
A drug-receptor complex is necessary to invoke a(n) ...
Definition
Effect/response
Term
Drug receptors are very..
Definition
specific
Term
Drugs (ligands) interact with
Definition
enzymes, nucleic acids, and membrane receptors
Term
Desensitization occurs when
Definition
you have too much drug hitting a receptor and you develop a tolerance.

Causes cells to protect themselves from too much drug. You lose the therapeutic affect.

this is a pharmacodynamic response
Term
Receptor Occupancy Theory
Definition
the magnitude of the effect is assumed to be directly proportional to the [drug]

Basically, the more drug, the more effect

Effect = Rmax x [D]/ Kd + [D]
Term
N.B. Drug
Definition
Receptor interaction not static, rather on/off interaction
Term
A Dose-Response Curve (DRC) plots..
Definition
the dose of a drug vs. the effect

it is a semi-log plot
Term
A Drug-Receptor (D-R) curve shows
Definition
potency, efficacy, and slope
Term
What are the two molecular properties drugs are classified on, according to their magnitude?
Definition
1. Affinity for the receptor (potency)
2. Efficacy once bound to the receptor
Term
Agonist has..
Definition
AFFINITY for the receptor and EFFICACY
Triggers 100% response

it binds to a receptor and elicits a response

Ex: Adrenaline causes 100% bronchial dilation
Term
Antagonist has
Definition
AFFINITY but NO efficacy
Term
a Partial agonist has
Definition
affinity and low efficacy

Ex: Ibuterol. Doesn't give 100% bronchial dilation
Term
Efficacy is
Definition
the maximal response produced by a drug
Term
Potency
Definition
Effective dose concentration
How much drug is required to elicit desired response

Usually the ED50
Term
Clinically, a drug that is more _ is more important than a drug that is _
Definition
efficient, potent
Term
A maximum agonist response can be achieved in the presence of a competitive antagonist if..
Definition
given at a high enough dose
Term
Competitive antagonism shifts the agonist D-R Curve to the right/left?
Definition
Right.
it decreases the potency, therefore requiring a larger drug concentration to overcome the agonist and achieve the desired affect
Term
An agonist can never overcome a _ antagonist
Definition
noncompetitive
Term
Factors that affect drug response
Definition
resistance, tolerance, tachyphylaxis
Term
Tolerance
Definition
a decrease in drug response during repeated administration
Term
Tachyphylaxis
Definition
ACUTE development of tolerance due to rapid repeated administration of some drugs
Term
Pharmacokinetic Tolerance is due to what?
Definition
a decrease in [drug] at its site of action

Ex: barbiturates, alcohol, phylbutazone
Term
Pharmacodynamic tolerance is
Definition
the reduced responsiveness to the drug at its site of action
Ex: amphetamine, caffeine, nicotine, morphine, barbiturates, alchol

usually drugs that affect behavior or psychological outlook
Term
Dose-Response Curve: Quantal responses
Definition
Shows the frequency with which a defined effect occurs in a population at a given dose

can express the cumulative frequency with which an effect occurs in a population at a given dose and all lower doses
Instead of measuring the degree of response, it measures # of people who have a therapeutic response at some level
Term
Therapeutic Index
Definition
frequency of desired response and toxic response at various doses

Therapeutic Index = toxic dose/ effective dose
Term
Small therapeutic index
Definition
small increase in dose is more likely to produce toxic effect
Term
Large therapeutic index
Definition
large increases in dose are less likely produce toxic effect
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