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Pharmacology (Subject) / Introduction (Lesson)

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• Antagonist (Def. + Characteristics) "A substance which interferes with or inhibits the physiological action of another". affinity no efficacy (no intrinsic activity)
• Pharmalogical Antagonism I: Competitive (reversible) antagonists Compete with agonist for binding to the active site of the receptor (e.g. enzyme) --> reduce its ability to produce a response   The extend of antagonism depends on the relative amount of agonist <--> antagonist  --> by increasing the amount of agonist the blocking effect of the antagonist can be surmounted --> full response can be restored (same efficacy) even though more agonist A is required (less potency) Effect lasts until the drug is metabolised (min to h)
• Pharmalogical Antagonism II: Non-competitive antagonist Occupe some of the receptor active sites/allosteric site irreversibly  The efficacy and potency is reduced --> the remaining receptors can't elicit a max response  Effect wears off when receptor is replaced (h to d)
• Pharmacokinetic antagonism Antagonist reduces concentrations of the agonist at its target --> reducing its absorption or distribution, increasing its metabolism or excretion 
• Physiological Antagonism Two drugs which have opposite actions in the body which tend to cancel one another (via different receptors)
• Different agonists (2) Full agonist produce a max response even by activiating only a proportion of their receptors --> spare receptors Partial agonist can't produce a max response even when occupying all receptors  --> low efficacy --> in the presence of a full agonist, a partial agonist can act as a partial antagonist  
• Tolerance and tachyphylaxis General on repeated administration of some drugs, increasing doses need to be given for the same effect --> receptor down-regulation, enhanced drug elimination (e.g. alcohol) Tolerance slow... Tachyphylaxis acute, sudden decrease in response to a drug after its administration
• Clinical trials heart of evidence-based medicine Ethics approval --> volunteers give their informed consent  Randomisation --> random allocation to test drug or placebo Double-blinded --> neither the subjects nor the experimentor know which formulation is which

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