Lecture_2-Basic_Pharmacological_Principles

Enabling the initiation of the action effect sequence

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Unformatted text preview: enabling the initiation of the action- effect sequence – Not so stable that it cannot be reversed • Selectivity, specificity and reversibility are due to the synchronous operation of a number of chemical bonds-not a single bond Drug-Receptor Interactions • Forces to hold it to receptor=chemical bonds- Ionic bonds: electrostatic attraction; transfer of electrons (- charged molecule binds to a + charged molecule & vice versa); rapid & relatively strong bond; can occur across distances; holds drug to receptor- Covalent bonds: sharing a pair of electrons; very strong bond (20 times stronger than ionic bond); accounts for stability of most organic molecules- Hydrogen bond: type of ionic bond with hydrogen (+ charged); weak bond but if multiple hydrogen bonds are formed high stability- Van der Waals forces: weak attractive forces between 2 neutral atoms; operate in close range; “final notches in key that open the door” Ionic bond Covalent bond Hydrogen bonds Quantitative aspects of drug action • Basic pharmacological principle: the degree of a drug effect produced by a drug is a function of the quantity of drug taken • Dose : amount of drug needed at a given time to produce a particular biological response – Amount of drug needed to achieve a particular concentration of a drug at the site of action – Factors of absorption, distribution, biotransformation, excretion • The concentration of a drug at its site of action depends not only on the dose administered but also on time (to get to and from the site of action) Quantitative aspects of drug-receptor interactions • Drug effect is a consequence of a reversible chemical or physiochemical reaction between a drug and a receptor biological change • Just as for enzymes, the Law of Mass Action applies to drug-receptor interactions: Drug + receptor drug-receptor complex Effect • Occupancy of receptors by a drug is proportional to the concentration of the drug and the concentration of free, unoccupied receptors – Magnitude of the pharmacological effect elicited by a drug should be directly proportional to the number of receptors occupied by the drug • AJ Clark’s quantification of dose-effect relationships assumes: – Law of mass action is applicable to reversible reactions between a drug molecule and one receptor – All receptors are identical and equally accessible to the drug – Intensity of the response to a drug is directly proportional to the number of receptors occupied by the drug and is a direct consequence of the drug-receptor interaction – Amount of drug that interactions with receptors is negligible compared to the amount of drug to which the receptors are exposed; effective drug concentration does not change during drug-receptor interaction • AJ Clark’s quantification of dose-effect relationships assumes: – Law of mass action is applicable to reversible reactions between a drug molecule and one receptor – All receptors are identical and equally accessible to the drug – Intensity of the response to a drug is directly proportional to the number of receptors occupied by the drug and is a direct consequence of the drug-receptor interaction...
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enabling the initiation of the action effect sequence –...

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