Drugs are broadly classified into following types depending on the purpose for which they are used.
1. Antipyretics
Chemical substances which are used to bring some of the common antipyretics.
Out of these antipyretics aspirin has been in common use, but because on hydrolysis it gives salicylic acid which causes bleeding in stomach, it should not be taken on empty stomach. Calcium and sodium salts of aspirin are highly soluble and less harmful.
2. Analgesics
Chemical substances used for relivering pain are called analgesics.
These are classified into two types:
(i) Non-narcotic analgesics (non-addictive analgesics)
Aspirin and paracetamol are the familiar examples of this type of analgesics.
Aspirin and paracetamol act both as antipyretics and fever. They give immediate relief from pain and fever. Aspirin inhibits the synthesis or prostaglindins which stimulate inflammation in the tissue and cause pain. Aspirin is also used for prevention of heart attacks as it has anti-blood clotting action.
Novalgin is the most widely used analgesic.
Some other analgesics are:
Butazolidine or phenyl butazone, ibuprofen, naproxen and diclofenac sodium or potassium.
(ii) Narcotics analgesics
In addition to the above analgesics certain narcotic analgesics like morphine, codeine, pethidine, hydrochloride, methadone, heroin etc. which are also used for analgesics. These do relieve the patient of pain but they attack the central nervous system and produce sleep and unconsciousness. Narcotics are mostly the products obtained from opium and marijuana plants.
Narcotic analgesics are mainly used for the relief of post operative pain, cardiac pain and pains in terminal cancer patients.
3. Antiseptics
Chemical substances which prevent the growth of micro-organisms or kill them but are not harmful to the living human tissues are called antiseptics. Antiseptics are used for the living tissues. These are supplied to wounds, ulcers and diseased skin surfaces. The antiseptics are usually incorporated in face powders, deodorants, breath purifiers, etc to reduce the odours which may result from the bacterial decomposition body or in the mouth.
Some of the compounds used as antiseptics are exemplified below:
(i) Dettol, a mixture of chloroxylenol (also known as parachlorometaxylenol) and terpineol, is a commonly used antiseptic for wounds, cuts, diseased skin surface etc.
(ii) Bithional is added to soaps to impart them antiseptic properties. Such soaps are used to reduce odour due to bacterial action on skin surface.
(iii) Iodine is also used as an antiseptic in the form of tincture of iodine i.e. a 2-3% solution of iodine in alcohol-water.
(iv) Hydrogen peroxide solution also has strong irritating antiseptic properties and is commonly used to clean wounds.
4. Disinfectants
Chemical substances which kill microorganisms or stop their growth but are harmful to human tissue are called disinfectants. Since these substances are harmful to human tissue, they cannot be applied directly to wounds. They are used to disinfect floors, toilets, etc. For example, phenol (1%), sulphur dioxide, etc.
Chlorine with concentrations of 0.2 to 0.4 ppm (parts per million) is used as a disinfectant for drinking water.
5. Transquilizers
These are substances which are used for the treatment of stress and mental diseases. These affect the central nervous system and induce sleep to the patients. Such compounds usually constitute sleeping pills. The transquilizers are also called psychotherapeutic drugs. The administration of these drugs makes the patient passive and helps to control their emotional distress which otherwise is likely to interfere with their normal functions.
Different transquilizers function by different mechanisms. Certain transquilizers function by deactivating the action of some enzyme. For example, antidepression drugs Iproniazid and Phenelzine act through such a mechanism.
6. Antimicrobials
Antimicrobials are the drugs which cure the diseases caused by micro-organisms such as bacteria and viruses.
Micro-organisms are very small organisms which can be seen only through a microscope. Any microorganism that causes a disease is called pathogen. Our body has a natural defence mechanism which protects our body from pathogenic microbes. Many body secretions either kill the microbes or inhibit their growth. Some examples are: hydrochloric acid in stomach; fatty acids and lactic acid in sweat and sebaceous secretions; lysozyme, a lipid splitting enzyme in tears, nasal secretions and saliva.
The search for chemicals that would adversely affect the invading bacteria but not the host began in the nineteenth century. The German bacteriologist Paul Ehrlich developed the medicine arsphenamine for the treatment of syphilis. He got Nobel prize for medicine in 1908 for this discovery.
7. Antibiotics
Chemical substances which are produced by micro-organisms (such as moulds and bacteria) and are capable of destroying other micro-organisms are called antibiotics. The first antibiotic, revealed by Alexander Fleming in 1929 from the mould Penicilium notatum, was penicillin. Penicillin is an effective drug for pneumonia, bronchitis, sore throat etc.
8. Antacids
One of the most common ailments associated with digestion is acid gastritis. It is due to surplus hydrochloric acid in the gastric juice. Medicines which remove the excess acid in the stomach and raise the pH to appropriate level are called antacids.