Antibiotics are chemical medicinal medicines of microbial, synthetic, or semi-synthetic origin that prevent the development of other bacteria at low concentrations.Classification of Antibiotics:On the basis of chemical structureOn the basis of originOn the basis of range of activity ( spectrum of activity)On the basis of mode of actionOn the basis of effects of their activityOn the basis of route of administrationSemi-synthetic antibiotics, such as Penicillin V, contain an original chemical molecule from a microorganism but have been further altered. Synthetic antibiotics, such as cephalosporins, are made entirely in a laboratory.