Amoxicillin is a penicillin antibiotic that fights bacteria. It fights many different things. Some examples are; tonsillitis, bronchitis, pneumonia, and infections of the ear, nose, throat, skin, or urinary tract. The drug can be used combined with Clarithromycin, or Biaxin to treat stomach ulcers caused by Helicobacter pylori infection. This combination is referred to as Lansoprazole or Prevacid.