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GENERAL INTRODUCTION(A) DrugThe word drug is derived from the French word “drogue” which means „a dryherb‟. It is the single active chemical entity present in a medicine that is used fordiagnosis, prevention, treatment/cure of a disease. This disease oriented definitionof drug does not include contraceptives or use of drugs for improvement of health.According to “WHO” a drug may be defined as “Any substance or product which isused or intended to be used for modifying or exploring physiological system aspathological status for the benefit of the recipient”.(B) PharmacologyPharmacology is the science of drugs. In a broad sense, it deals withinteraction of exogenously administered chemical molecules (drugs) with livingsystem. It encompasses all aspects of knowledge about drugs, but most importantlythose that are relevant to effective and safe use for medicinal purposes. Forthousands of years most drugs were crude natural products of unknown compositionand limited efficiency. Only the over effects of these substances on the body wererather imprecisely known, but how the same were produced was entirely unknown.Over the past 100 years or so, drugs have been purified, chemically characterizedand a vast variety of highly potent and selective new drugs has been developed.The two main divisions of pharmacology are pharmacodynamics and pharmacokinetics.(a) Pharmacodynamics: It is derived from the Greek word “dynamic” meansPower. What the drug does to the body ? This includes physiological andbiochemical effects of drugs and their mechanism of action at macromolecular/ sub cellular organ systems.7General Introduction …..