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Pharmacodynamics - Receptor Theory (Drug receptor interactions (Terms…
Pharmacodynamics - Receptor Theory
Drug targets
Membrane receptors
Ion channels
Carriers / Transporter molecules
Enzymes
Receptors
Bind to:
Agonists
Have:
Efficacy
Affinity
Inverse agonists
Cause a reduction in activity of the receptor
Antagonists
Have:
NO Efficacy
Affinity
Non-competitive
Allosteric
Pharmacokinetic
Signaling blockade
Physiological
Chemical
Spare
Cells have extra receptors than what is required for maximal response
Drug receptor interactions
Dissociation constant (KD)
Concentration of drug required to occupy 50% of receptors
50% Effective dose (ED50)
Concentration of drug required to illicit 50% maximal biological response
Terms
Efficacy
Measure of the maximal effect of a drug at saturating concentrations
Potency
amount of drug required to achieve a specific level of response
Synergism
Overall effect is greater than sum of individual effects
Desensitization
Gradual diminishing response to drug
Due to:
Changes in receptors
Altered conformation
Uncoupling of associated signaling molecules
Translocation of receptors
Exhaustion of mediators
Altered drug metabolism
Physiological adaptation
Therapeutic index (TI)
LD50 / ED50
Certain safety factor (CSF)
LD1 / ED99
Receptor antagonism
Reversible
Shifts binding curve to the right
Administering more of the drug will produce the same tissue response
Irreversible
Permanently lowers the number of available receptors for the drug
Lowers the saturation point of the binding curve
Partial
Unable to reach maximal response