CAS No.:69-52-3 assay:99% Ampicillin is a beta-lactam antibiotic that has been used extensively to treat bacterial infections since 1961. It is considered part of the aminopenicillin family and is roughly equivalent to amoxicillin in terms of spectrum and level of activity.It can sometimes result in allergic reactions that range in severity from a rash (e.g. patients with mononucleosis) to potentially lethal anaphylaxis.