THE CLASSIFICATION OF DRUGS

  Drugs may be classified in a number of ways. One way is in terms of the nature of the disease that they are being used to treat. Thus there are compounds that are used to treat infectious diseases. Second, there are compounds that are used to treat cancers and third, non-infectious 1 diseases. The chemistry of infectious diseases is concerned with the development of drugs to injure an invading organism with minimal injury to the host. The targets are often the differences between the viral, bacterial, fungal or parasitic cells and those of man. This is the area of the antibiotics. The medicinal chemistry that is used in the treatment of cancers involves the use of drugs to destroy an aberrant cell within the host. The targets of cancer chemotherapy are the differences between the rapidly proliferating cancer cells and normal cells. Cancer chemotherapy is often used in conjunction with other forms of treatment such as radiotherapy. The chemistry of non-infectious diseases involves a study of the selective action of a drug on one cell or receptor in the host. In some cases the drugs are developed as mimics of natural hormones. The drugs that are used in the treatment of non-infectious diseases can be further sub-divided in terms of their targets. There are a group of hormones known as neurotransmitters that are formed at nerve endings and convey the consequences of a nerve impulse to a receptor or an effector cell. There are drugs, which affect primarily the neurotransmitters in the central nervous system including the brain and the spinal cord. These include the psychotropic agents, the anti-depressants, hypnotics and analgesics. There are those agents, which affect the peripheral nervous system including the local anaesthetics. Another group of substances are those, which affect the circulatory system acting as anti-hypertensive and anti-thrombotic agents. These may interact with local hormones. These are a family of compounds that have a metabolic or endocrine target. These are compounds that are modifications of circulatory hormones that may be used as oral contraceptives or to correct a hormone deficiency. Finally there are those compounds, which target the immune system such as the immunosuppresive agents. However there is an overlap between these classes and a compound may show several types of biological activity. The pattern of usage and the length of time over which a drug may be administered varies between the classes. Hence the extent to which sideeffects can be tolerated varies quite widely. For example, an antibiotic may be given for a few days while a compound, which is given to correct a hormone deficiency or as an immunosuppresive agent may be administered for years.