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Lecture8 100717172142-phpapp01
- 3. Receptors and Receptor Site
- 4. Continue… • Receptor down-regulation: A phenomenon whereby an agonist, after binding to a receptor, actually induce a decrease in the number of these receptors available for binding • Receptor Up-regulation: The opposite of the above, involves an agonist-induced increase in the number of receptors.
- 5. Continue… • Affinity: The ability of the drug to combine with a receptor. A ligand of low affinity requires a higher concentration to produce the same effect as a ligand of high affinity. Both agonists and antagonists have affinity for the receptor. Efficacy: Describe the relative intensity with which agonist vary in the response they produce when occupying the same number of receptors and with the same affinity
- 6. Continue… • Potency: Refers to the dose of a drug required to produce effect of given magnitude as compared to a standard reference. Potency is dependent on both affinity and efficacy. • Tolerance: Decrease of the intensity of the response to a given dose over time
- 7. Stereochemistry of Drug Action
- 12. The influence of configuration on ADME • Absorption:
- 13. Active Transport: • (-)Norgestrel is absorbed at twice the rate of (+)Norgestrel • L-Dopa is more rapidly absorbed in comparison to D- Dopa • Passive diffusion: • No difference in absorption between enantiomers • Racemates may be absorbed at a rate that is different to their pure individual enantiomers
- 14. Distribution • Stereoselectivity appears to have little influence on the transport of stereoisomers through the circulatory system. • Some enantiomers prefer to bind to a specific plasma protein (R-Propanalol prefers to bind to human albumin while S-Propanalol prefers alpha-acid glycoproteins)
- 15. Metabolism
- 16. • S-Indacrinone plasma half-life is 2-5 hours • R-Indacrinone plasma half-life is 10-12 hours
- 17. Extraction • Modest stereoselectivity has been reported in the renal excretion of these drugs
- 18. Next Lecture • Drug Metabolism
- 19. THE END