Penicillin is a beta-‐lactam antibiotic and can therefore cross-‐react with other beta-‐lactam antibiotics Ceftriaxone (3 rd). • Cefotaxime (3 rd) o Cross-‐reactivity rates between cephalosporins and penicillin allergy range from 0.17 to. 8.4%. canadian-pharmacyu.com buying viagra online