PHC 222 Part(I) Dr. Huda Al Salem Lecture (7). Factors that affect the efficacy 2- Concentration-Response Curves: Agonist Antagonist Partial agonist Desensetization.

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Presentation transcript:

PHC 222 Part(I) Dr. Huda Al Salem Lecture (7)

Factors that affect the efficacy 2- Concentration-Response Curves: Agonist Antagonist Partial agonist Desensetization

Concentration-Response Curve To get a quantitative information concerning the dose- response relationship of any drug.. they study the effect of the drug on an isolated tissue (in vitro). Examples: guinea big ileum or atria, rabbit jejunum, rat atria, canine coronary artery….etc

Concentration-Response Curve AGONIST CRC: The response due to an agonist increases with increasing concentration of the agonist until it reaches a maximum. At this point, further increase in dose have no further effect on the response. How to calculate the Dose of the drug?

Concentration-Response Curve

EC 50 Is the concentration of a compound where 50% of its maximal effect is Observed. EC 50 value of a drug will depend on the biological effect being studied. Example:

Concentration-Response Curve Agonist CRC is used during preclinical drug development to compare the potency of the different analogues of a lead compound. Potency is a measure of drug activity It is proportional to affinity & efficacy

Concentration-Response Curve AGONIST CRC: 1- Agonists with similar structures acting on the same receptor will exhibit similar plots

Concentration-Response Curve AGONIST CRC: 2- The slopes of these plots are not always similar

Concentration-Response Curve ANTAGONIST CRC:

Concentration-Response Curve ANTAGONIST CRC: Antagonists inhibit the action of an agonist.

Concentration-Response Curve Two Types of antagonists present 1- Competitive 2- Non-competitive

Concentration-Response Curve Competitive antagonistNon-competitive antagonist Non-covalent bonds, reversible Covalent bonds, irreversible Its effect can be reversed by increasing the concentration of the agonist The action is not dependent on the concentration of the agonist

Concentration-Response Curve PARTIAL AGONIST : They are compounds that act as both agonists & antagonists How? They act as antagonists by preventing endogenous ligands from binding to their receptors. But their binding to the receptor results in a weak activation of the receptor. Why? 1- There is no perfect fit to the receptor site so does not cause enough change in receptor conformation.. 2- It has a structure that can bind to receptor in two different ways

Concentration-Response Curve DESENSETIZATION Is the loss of biological response after continuing or increasing dose of a drug. Other names.. Tachyphylaxis or drug tolerance It appears that the drug starts by acting as a full agonist but its repeated use results in partial agonistic action. Rate theory is the only explanation of this phenomenon