The words ‘medicine’ and ‘drug’ are often used in our country to mean the same substances: any substance, manufactured artificially, which can help recovery from sickness, relieve symptoms or modify a natural process in the body. A medicine is often a mixture of several chemical compounds. Even if it has only one active component or compound often other substances are used as fillers or binders to give it bulk.
Chemistry, the science related to chemical substances, provides us the tools to make and study the substances that are the constituents of almost all medicines. The past hundred years or so, ever since the advent of organic chemistry, many chemical compounds have been discovered in nature that are effective for curing diseases.
Modern chemistry has also made it possible to synthesize several medicines using methods of organic chemistry.
There are very many medicines that come under each of these groups. Often several chemical compounds that make a particular group of medicines, say antibiotics have similar chemical structure. Since the medicines in a particular group are effective for treating a particular type of ailment or disease, their mode of action can also be very similar. But, the methods used to isolate a medicine from its natural sources or to synthesize it are most often very different.
Classification of drugs:
Drugs are broadly classified into two main classes on the basis of their therapeutic action.
Pharmacodynamic agents deal with the study of the biochemical and physiological effects of drugs and the mechanisms of their actions including the correlation of actions and effects of drugs with their chemical structure.
These drugs act selectively on any system of the body like the central nervous system (CNS), peripheral nervous system, cardiovascular system, hematapoietic system, renal system etc. The pharmacodynamic agents interact with specific receptors in the body tissues and regulate their biochemical functions. These are classified into various types. The site of the action of the drug along with the commonly used drugs is indicated in the table.
The pharmacological activity of a drug allows a rational basis of classification. They are thus classified as analgesics, drugs which give relief from pain; antimalarials which act against malarial parasite, anti bacterial, drugs which either kill or reduce the growth of harmful bacteria, anesthetics, drugs which produce anesthesia, insensitive to pain, hypnotics, sedatives and tranquilizers which act on the central nervous system and produce sedation and sleep etc.