Antibiotics or antibacterials are a type of antimicrobial used specifically against bacteria,[1][2] and are often used in medical treatment of bacterial infections.[1] They may either kill or inhibit the growth of bacteria. Several antibiotic agents are also effective against a number of fungi, protozoans and some are toxic to humans and animals, even when given in therapeutic dosage. Antibiotics are not effective against viruses such as the common cold or influenza, and may be harmful when taken inappropriately.

Antibiotics revolutionized medicine in the 20th century, and have together with vaccination lead to the near eradication of diseases such as tuberculosis in the developed world. Their effectiveness and easy access led to overuse, especially in live-stock raising, prompting bacteria to develop resistance. This has led to widespread problems with antimicrobial and antibiotic resistance, so much as to prompt the World Health Organization to classify antimicrobial resistance as a "serious threat [that] is no longer a prediction for the future, it is happening right now in every region of the world and has the potential to affect anyone, of any age, in any country".[3]

The era of antibacterial chemotherapy began with the discovery of arsphenamine, first synthesized by