Patients and a thorough medical history is recommended prior to prescribing this medication. It is important that you tell your doctor and pharmacist if you are allergic or feel that you might be allergic to penicillin, you should avoid taking Cephalexin because of the chance that you will be allergic to penicillin, you should avoid taking Cephalexin because of the chance that you will be allergic to penicillin, you should avoid taking Cephalexin because of the chance that you will be allergic to it too.