Lecture_2-Basic_Pharmacological_Principles

Position of the curves along the x-axis is indicative

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Unformatted text preview: Position of the curves along the X-axis is indicative of their relative affinities (higher affinities lie closer to the Y-axis) C= Y Kd(100-Y) Want to occupy 50% of the receptors, C= 50 , C= 1 Kd (50) Kd Interpreting dose-effect curves • Dose-response curves can also provide a measure of potency ; the dose needed to produce a particular effect of a given intensity • Potency also varies inversely with the magnitude of dose – depends on inherent ability of the drug to bind to a receptor (affinity=Kd) – Depends on factors regulating how much drug reaches the site of action – Comparative expression of drug activity at a particular site ( relative to a standard of reference ) Interpreting dose-effect curves: Full vs. partial agonists • Partial agonists elicit a biological response upon binding but the magnitude of the response ( efficacy ) is reduced NOTE: efficacy is independent of affinity (in this example, the partial agonist has a much lower Bmax than the full agonist, but the Kd is lower than the full agonist) Drug Antagonism • Agonists: Drugs that bind to a receptor and induce a biological response • Antagonists: drugs that interaction with a receptor but do not trigger a biological response • Competitive antagonists: drug binds reversibly with the same site as the active drug (or agonist) and can be displaced from the site by excessive agonist – Decreases the number of available receptors with which the agonist (drug) can interact shift to the right in the dose-response function Quantitative Aspects of Antagonism • Competitive antagonists: drug binds reversibly with the same site as the active drug (or agonist) and can be displaced from the site by excessive agonist – Decreases the number of available receptors with which the agonist (drug) can interact results in a reduction in agonist binding Ki =Concentration of drug that results in 50% reduction in radioligand binding i.e., dose at which 50% of the receptors are blocked by antagonist Expt: Incubate radioactive agonist with increasing concentration of unlabeled antagonist Antagonists with LOWER Ki’s are more potent than antagonists with HIGHER Ki’s (so you can use less antagonist to block a particular drug/neurotransmitter effect) Drug Antagonism • Non-competitive antagonists: its effects cannot be overcome completely by increasing agonist concentrations; antagonizes drug effect by combining with different sites as the active drug – Prevents drug from inducing 100% of maximum response decrease in maximum response – Decreases the number of available receptors with which the agonist (drug) can interact shift to the right in the dose-response function – Larger reduction in slope greater non- competitive antagonism Full inverse agonist-Full=drug binds with 100% efficacy to the receptor-Inverse=opposite-Agonist=drug that elicits a biological effect A drug that binds with full efficacy to a receptor but elicits a biological effect that is opposite to that produced by a traditional full agonist Often mistaken for antagonists because a full inverse agonist blocks the effects of an agonist but the mechanism is completely different...
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Position of the curves along the X-axis is indicative of...

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