Always ask a doctor and pharmacist before taking any kind of antibiotic. Specifically tell your doctor that you are allergic to Penicillin so that they know. I am not allergic, but my mother and sister developed a penicillin allergy later in life, so my doctor naturally keeps me off of it as a precaution. I rarely use an antibiotic but if I absolutely have to I always double check. I'm not sure about others, but cephalexin I am pretty sure does not have penicillin in it.