Antibiotics, also called antibacterials, are a type of antimicrobial 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. Sometimes the term antibiotic (which means “opposing life”) is used to refer to any substance used against microbes, synonymous with antimicrobial. Some sources distinguish between antibacterial and antibiotic; antibacterials are used in soaps and disinfectants, while antibiotics are used as medicine.Antibiotics revolutionized medicine in the 20th century.

However, their effectiveness and easy access have also led to their overuse, prompting bacteria to develop resistance. Antibiotics are used to treat or prevent bacterial infections, and sometimes protozoan infections. Antibiotics are used to prevent infection in cases of neutropenia particularly cancer-related.