Antimicrobial compounds include synthetics, semisynthetics and antibiotics.  Antimicrobial agents are used exclusively for the treatment of disease.

Antibiotics are compounds produced naturally by living organisms to inhibit the growth of other organisms that compete for food and space.  Antibiotics that are chemically altered to give them different characteristics are said to be semisynthetic.

Synthetic compounds are completely man-made.  Examples include protease inhibitors, quinolones and fluoroquinolones.