An antibiotic is given for the treatment of an infection caused by bacteria. It is a type of medication that destroys or slows down the growth of bacteria. However, with increased knowledge of the causative agents of various infectious diseases, antibiotics has come to denote a broader range of antimicrobial compounds, including anti-fungal and other compounds.But, antibiotics are not effective against viruses

Although there are a number of different types of antibiotic they all work in one of two ways: they are either bactericidal or bacteriostatic.  A bactericidal antibiotic kills the bacteria. Penicillin is a bactericidal. A bactericidal usually either interferes with the formation of the bacterium's cell wall or its cell contents and a bacteriostatic antibiotic stops bacteria from multiplying. Sometimes antibiotics are given to prevent infection, and then it is called 'prophylactic' use of antibiotics. For instance they are commonly used before bowel and orthopedic surgery as a prophylactic.

There is a concern worldwide that antibiotics are being overused. This is one of the major factors that contribute to the growing number of bacterial infections which are becoming resistant to antibacterial medications. Hence, if there is an infection it is important to know whether it is caused by bacteria or a virus. Most upper respiratory tract infections, such as the common cold and sore throats are generally caused by viruses - antibiotics do not work against these viruses. Many a times it is also seen that antibiotics are redundantly wasted on diarrhea without proper examining its causative factor. Hence a thorough examination of the causative agent before taking medicine is essential.