I may need cephalosporin therapy with a suspected penicillin allergy. how does it work? do i take a 3rd generation by mouth and sit in an er waiting room with a buddy and an epipen (epinephrine)?

Don't overreact: Allergies to cephalosporins are very rare, even in people with penicillin allergy. I doubt it is necessary to stay in an emergency room or even a doctor's office, or to have an WpiPen at hand. Discuss with the doctor prescribing the antibiotic.

Penicillin allergy: Among all patients reporting penicillin allergy, 85 to 90% will tolerate a penicillin, either because they were never allergic or because they had an earlier allergy that subsequently resolved. Among penicillin skin test-positive patients, approximately 2% will react to a cephalosporin.