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Drug-Receptor Interactions and Pharmacodynamics (cont.)

Drug-Receptor Interactions and Pharmacodynamics (cont.). Enzyme-linked receptors (Insulin Receptors). Dimers or multisubunits Lasts min to hrs Ex., epidermal growth factor(EGF), platelet-derived growth factor (PDGF), atrial natriuretic peptide (ANP), insulin & others.

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Drug-Receptor Interactions and Pharmacodynamics (cont.)

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  1. Drug-Receptor Interactions and Pharmacodynamics (cont.)

  2. Enzyme-linked receptors(Insulin Receptors) • Dimers or multisubunits • Lasts min to hrs • Ex., epidermal growth factor(EGF), platelet-derived growth factor (PDGF), atrial natriuretic peptide (ANP), insulin & others

  3. Intracellular receptors • Takes hours to days to give response • Examples: steroid H, structural pts, Es, RNA & ribosomes

  4. Characteristics of Signal Transduction • Signal Amplification e.g. albuterol • Spare receptors insulin spare Rs = 99% β-adrenoceptors = 5-10%

  5. Desensitization, & Down-Regulation of Receptors Tachyphlaxis: repeated administration of the agonist lead to decrease in responsiveness of Rs Refractory Up-regulation of receptors

  6. Dose-Response Relationships Graded dose-response curve (DRC) Potency amount of drug required to produce a given response & used to determine ED50 Candesartan 4 – 32 mg Irbisartan 75 – 300 mg Efficacy: the magnitude of response Maximal efficacy Emax

  7. Dose-Response Relationships

  8. Effect of Drug Concentration on Receptor Binding

  9. Relationship of Drug Binding to Pharmacologic Effect • Kd value used to determine affinity • The higher the Kd, the weaker the interaction, the lower the affinity • The magnitude of response is proportional to the amount of Rs bound • Emax represent full occupation of Rs • Affinity should be related to potency of drug for causing physiologic response

  10. Intrinsic activity represents the ability of a D to act as: I- Full Agonists intrin. activity =1 II- Partial Agonists intrin. activity > 0 & <1 III- Inverse Agonists Spontaneous conversion from R to R* intrin. activity < 0

  11. Effects of Partial Agonists

  12. Competitive antagonism Competitive --- Surmountable Competes with agonist in reversible fashion for same receptor site Necessary to have higher concentration of agonist to achieve same response

  13. Noncompetitive antagonism Noncompetitve --- Insurmountable Antagonist binds to a site different to that of an agonist No matter how much agonist -- antagonism cannot be overcome

  14. Antagonists I- Competitive Antagonists II- Irreversible Antagonists III- Allosteric Antagonists IV- Functional or Chemical Antagonists

  15. Therapeutic Index

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