Please consult your physician before taking any medication. What is amoxicillin? Amoxicillin is an antibiotic in the penicillin group of drugs. It fights bacteria in your body. Amoxicillin is used to treat many different types of infections caused by bacteria, such as ear infections, bladder infections, pneumonia, gonorrhea, and E. coli or salmonella infection. Amoxicillin is also sometimes used together with another antibiotic called clarithromycin (Biaxin) to treat stomach ulcers caused by Helicobacter pylori infection. This combination is sometimes used with a stomach acid reducer called lansoprazole (Prevacid). Amoxicillin may also be used for purposes other than those listed in this medication guide.