What is Augmentin? Augmentin is a penicillin antibiotic. Amoxicillin/clavulanic acid is a combination penicillin-type antibiotic used to treat a wide variety of bacterial infections. It works by stopping the growth of bacteria. This antibiotic treats only bacterial infections. It will not work for viral infections (such as common cold, flu). Unnecessary use or misuse of any antibiotic can lead to its decreased effectiveness.