Penicillins are a type of antibiotic derived from Penicillium fungi. An antibiotic is a type of medicine that inhibits the growth of, or kills, bacteria.
Penicillin G (also called benzylpenicillin) was discovered by accident in 1928. Alexander Fleming, he observed that the areas of bacteria near the mold were dying. He isolated the substance from the mold that was killing the bacteria and called it penicillin.
Another naturally occurring penicillin, penicillin V was later isolated from the same mold. All other penicillins are semi-synthetic (made by modifying the structure of the original naturally occurring penicillins).

Drug classes:

• aminopenicillins
• antipseudomonal penicillins
• beta-lactamase inhibitors
• natural penicillins
• penicillinase resistant penicillins