Antibiotics are substances of natural or semi-synthetic origin that inhibit the growth of living cells, most often prokaryotic or protozoa.

Fully synthetic drugs that do not have natural analogues and have an inhibitory effect on bacterial growth similar to antibiotics have traditionally been called not antibiotics, but antibacterial chemotherapy drugs. In particular, when only sulfonamides were known from antibacterial chemotherapy drugs, it was customary to talk about the entire class of antibacterial drugs as “antibiotics and sulfonamides”.

However, in recent decades, in connection with the invention of many very powerful antibacterial chemotherapeutic agents, in particular fluoroquinolones, approaching or exceeding the activity of “traditional” antibiotics, the concept of “antibiotic” has begun to erode and expand and is now often used not only in relation to natural and semi-synthetic compounds, but also to many strong antibacterial chemotherapy drugs.