In 1966, the World Health Organization (WHO) defined drugs as “any substance or product used or intended to modify or explore physiological systems or pathological states for the recipient’s benefit, either therapeutic or diagnostic benefits.” Clinicians use drugs, which are chemical substances, to diagnose, prevent, or cure diseases and to affect living organisms.So the safe use of drugs needs sound knowledge of their various aspects such as mechanism of action, doses, routes of administration, adverse drug effects, toxicity, and drug interactions.

• General pharmacology involves the aspects of sources of drugs, route of administration of drugs, absorption of drugs and factors affecting them, their distribution, biotransformation, and excretion. It also involves the mechanism by which the drug is acting with the receptor, the toxicity of the drug, and preclinical and clinical evaluation.