What's a good antibiotic to take if your allergic to penicillin?

If you just had a rashfrom penicillin then cephalosporins like Keflexwould be fine. If immediate hypersensitivityto penicillin, like hivesor anaphylaxisyou should avoid all penicillins, cephalosporins and probably all carbepems (like imipenem). You can take all other antibiotics.