1. An antibiotic (from ancient Greek αντιβιοτικά, antibiotiká), also called an antibacterial, is a type of antimicrobial[1] drug used in the treatment and prevention of bacterial infections. They may either kill or inhibit the growth of bacteria. A limited number of antibiotics also possess antiprotozoal activity. Antibiotics are not effective against viruses such as the common cold or influenza; drugs which inhibit viruses are termed antiviral drugs or antivirals rather than antibiotics.

Antibiotics are used to treat or prevent bacterial infections,[14] and sometimes protozoan infections. (Metronidazole is effective against a number of parasitic diseases). When an infection is suspected of being responsible for an illness but the responsible pathogen has not been identified, an empiric therapy is adopted.[15] This involves the administration of a broad-spectrum antibiotic based on the signs and symptoms presented and is initiated pending laboratory results that can take several days.[14][15]

When the responsible pathogenic microorganism is already known or has been identified, definitive therapy can be started. This will usually involve the use of a narrow-spectrum antibiotic. The choice of antibiotic given will also be based on its cost. Identification is critically important as it can reduce the cost and toxicity of the antibiotic therapy and also reduce the possibility of the emergence of antimicrobial resistance.[15] To avoid surgery, antibiotics may be given for non-complicated acute appendicitis.[16]

Antibiotics may be given as a preventive measure and this is usually limited to at-risk populations such as those with a weakened immune system (particularly in HIV cases to prevent pneumonia), those taking immunosuppressive drugs, cancer patients and those having surgery.[14] Their use in surgical procedures is to help prevent infection of incisions. They have an important role in dental antibiotic prophylaxis where their use may prevent bacteremia and consequent infective endocarditis. Antibiotics are also used to prevent infection in cases of neutropenia particularly cancer-related.

"A drug which used to destroy diseases carrying microorganism by local application on skin, mucosa or cavities is called as antiseptic."

Thus, they do not impart any effect on body tissues as they applied only on infected surface. They can be used for viral, bacterial infection as well as for protozoal agents. The active chemical ingredients of antibiotics can applied directly to the affected area for either killing microorganisms or for inhibiting their growth. The use of antiseptic for sterilization in surgery was first given by Joseph Lister in 1867. He used carbolic acid (Phenol) for that purpose. Later many antiseptics like alcohol, chlorine, iodine are used for different purpose to make surface bacteria free. Because of the ability to inhibit the growth of microorganism, antiseptics are widely used in hospital and other health care centers for hard surface applications.

Generally antiseptics have broad spectrum antimicrobial activity i.e. they are active on various microorganisms. Like antibiotics, antiseptics are not much specific in their interaction with microorganisms like bacteria. Some antiseptics like Chlorhexidine (CHX) have limited specificity and active on both Gram-positive and Gram-negative bacteria. This antiseptic involves in the inhibition of cell attachment and limits the growth. This antiseptic has much less potent compare to antibiotics like doxycycline or minocycline. Thus antibiotics and antiseptics are quite differing in their potency and the specificity of their interactions with microbes.

Mode of action of antiseptics

Antiseptic like Chlorhexidine (CHX) contains a positively charged hydrophobic and lipophilic molecule which can combine with the molecules of phospholipids and lipo-polysaccharides on the cell membrane of microorganism.

Sulfa drug, also called sulfonamide, any member of a group of synthetic antibiotics containing the sulfanilamide molecular structure. Sulfa drugs were the first chemical substances systematically used to treat and prevent bacterial infections in humans. Their use has diminished because of the availability of antibiotics that are more effective and safer and because of increased instances of drug resistance. Sulfonamides are still used, but largely for treating urinary tract infections and preventing infection of burns. They are also used in the treatment of certain forms of malaria.