Ampicillin and amoxicillin are broad-spectrum penicillins, which means they kill many kinds of bacteria. The two are often interchangeable. When you see a recommendation for ampicillin, you will often be able to use amoxicillin in its place, in the correct dose (see below).
Ampicillin and amoxicillin are very safe and are especially useful for babies and small children. They are both useful in treating pneumonia or ear infections. Ampicillin is also useful in treating meningitis and other severe infections in newborns.