Antibiotics (from Greece: anti = against, bios = live) are drugs used to treat bacterial infections. Antibiotics are almost exclusively effective against bacterial infections. Some antibiotics are also effective against some protozoan infections. Antibiotics have no effect on viruses. Antibiotics that kill bacteria are called bactericidal, and those that only prevent them from multiplying are called bacteriostatic.
Antibiotics can also be classified based on the spectrum of activity: Narrow-spectrum antibiotics are more specific and only active against certain groups or strains of bacteria. The advantage of this is that it interferes less with the body’s own beneficial bacterial system. Broad-spectrum antibiotics instead inhibit a wider range of bacteria. Broad-spectrum antibiotics are often used when the potential causes of infection cannot be reliably inferred (e.g., nosocomial infections).
Antibiotic treatments can be given: a) orally: tablets, capsules or solutions b) intravenously c) topically e.g. as a cream or drop.