Please consult your physician before taking any medication. Ampicillin Generic 500mg 20 Caps Ampicillin 500mg 20 Caps Generic Name: ampicillin (am pi SIL in) Brand Names: Omnipen, Principen, Totacillin What is ampicillin? Ampicillin is an antibiotic in the penicillin group of drugs. It fights bacteria in your body. Ampicillin 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. Ampicillin may also be used for purposes other than those listed in this medication guide.