6-amino-penicillanic acid is a common parent amine of various penicillins. 6-amino-penicillinic acid possesses definite antibacterial properties but these are much lower order than these of benzylpenicillin. It is destroyed by penicillinase (Beta-lactamase). The first penicillins to appear as derivatives of 6-APA were in fact phenethicillin and propicillin.

Amoxicillin is one of the widely prescribed antibacterial agents, which was discovered by scientists at Beecham Research Laboratories in 1972. In the US GlaxoSmithKline markets it under the original brand name Amoxil. It is the first line treatment for middle ear infections. It is also used for strep throat, pneumonia, skin infections, and urinary tract infections it is taken by mouth. Amoxicillin inhibits the third and final stage of bacterial cell wall synthesis by preferentially binding to specific penicillin-binding proteins (PBPs) that are located inside the bacterial cell wall. This results in a formation of defective cell wall and a cell death. Common side effects include nausea and rash. It may also increase the risk of yeast infections and, when used in combination with clavulanic acid, diarrhea. It should not be used in those who are allergic to penicillin.