Amoxicillin is a penicillin antibiotic used to treat bacterial infections such as tonsillitis, bronchitis, sinusitis, pneumonia, and infections of the ear, nose, throat, skin, or urinary tract. Amoxicillin clavulanate is a combination of amoxicillin and clavulanate potassium. The amoxicillin fights bacteria, and the clavulanate potassium helps prevent certain bacteria from becoming resistant to amoxicillin.