Amoxicillin is a penicillin antibiotic. Amoxicillin is used to treat many different types of infections caused by bacteria, such as ear infections, bladder infections, pneumonia, and E. coli or salmonella infection. Amoxicillin is also sometimes used together with another antibiotic called clarithromycin to treat stomach ulcers caused by Helicobacter pylori infection. This combination is sometimes used with a stomach acid reducer.Brand may vary.