PHARMACOLOGY
11th October 2021
CHAPTER 1: INTRODUCTION: THE NATURE
OF DRUGS & DRUG DEVELOPMENT &
REGULATION
Pharmacology can be defined as the study of substances that interact with living
systems through chemical processes.
Medical pharmacology, which is often defined as the science of substances used to
prevent, diagnose, and treat disease.
Toxicology is the branch of pharmacology that deals with the undesirable effects of
chemicals on living systems.
Pharmacogenomics—the relation of the individual’s genetic makeup to his or her
response to specific drugs.
GENERAL PRINCIPLES OF PHARMACOLOGY:
THE NATURE OF DRUGS:
Drug may be defined as any substance that brings about a change in biologic function
through its chemical actions.
The drug molecule interacts as an agonist (activator) or antagonist (inhibitor) with a
specific target molecule called (receptor).
Chemical antagonists may interact directly with other drugs.
Osmotic agents interact almost exclusively with water molecules.
Hormones are drugs that are synthesized within the body
Xenobiotics are chemicals not synthesized in the body
Poisons are drugs that have almost exclusively harmful effects
Toxins are poisons of biologic origin
The Physical Nature of Drugs:
a drug molecule must have the appropriate size, electrical charge, shape, and atomic
composition to be able to interact with its target receptor.
A useful drug must be able to be transported from its site of administration to its site of
action efficiently
, A useful drug must be inactivated or excreted from the body at a reasonable rate after
its appropriate action
Many organic drugs are weak acids and bases
pH differences in different parts of the body alters the degree of ionization of weak
acids and bases
Drug Size:
most drugs have molecular weights between 100 and 1000
To fit only to one type receptor, a drug must be in unique shape, charge and other
properties, and it should be at least 100 MW units in size.
Drugs larger than 1000 MW do not diffuse readily between body compartments
Large drugs (e.g., proteins) must be administered directly into the compartment where
they have their effect.
Drug Reactivity & Drug-Receptor Bonds:
Drugs interact with receptors by means of covalent, electrostatic, and hydrophobic
forces.
o Highly reactive strong covalent bond-forming examples:
acetylsalicylic acid (aspirin) + cyclooxygenase: in platelets
DNA-alkylating agents used in cancer chemotherapy
o Electrostatic bond-forming examples:
Permanently charged ionic molecules
Weak hydrogen bonds
Dipole interactions (e.g., Van der Waals forces)
o Hydrophobic bond-forming examples:
Interactions of highly lipid-soluble drugs
Interaction of drugs with walls of receptors (pockets)
Drug Shape:
chirality (stereoisomerism): more than half of all useful drugs are chiral molecule
because enzymes are usually stereoselective, one drug enantiomer is often more
susceptible than the other to drug- metabolizing enzymes
Rational Drug Design:
Rational design of drugs implies the ability to predict the appropriate molecular
structure of a drug on the basis of information about its biologic receptor
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