Penicillins and cephalosporins are also the most common causes of drug allergy. About 10 percent of Americans report having an allergy to penicillin or a related antibiotic. Before using penicillin V, tell your doctor if you are allergic to cephalosporins such as Ceclor, Ceftin, Duricef, Keflex, and others, or if you have asthma, kidney disease, a bleeding or blood clotting disorder, a history of diarrhea caused by taking antibiotics, or a history of any type of allergy. Penicillin allergy is an abnormal reaction of your immune system to the antibiotic drug penicillin. Penicillin is prescribed for treating various bacterial infections. Penicillin is prescribed for treating various bacterial infections. Amoxicillin is effective against most of the same strains as penicillin, but is more effective against otitis media (ear) infections, endocarditis (heart valve infections), and infections caused by enteroccocus strains. Amoxicillin is in the same family of antibiotics as penicillin. Your allergist / immunologist can review your history and perform skin testing to help you understand if you are still allergic to amoxicillin. This skin testing is similar to penicillin skin testing. People who have a suspected penicillin (or closely related antibiotic) allergy and require penicillin to treat a life-threatening condition for which no alternate antibiotic is appropriate. People who have frequent infections and have suspected allergies to many antibiotics, leaving few options for treatment. Amoxicillin and penicillin are two of many antibiotics on the market today. They’re actually in the same family of antibiotics, called the penicillin family. Hypersensitivity reactions are the major problem in the use of penicillins. True penicillin allergy is rare with the estimated frequency of anaphylaxis at 1-5 per 10 000 cases of penicillin therapy. I'm very allergic to penicillin. Should it be safe use amoxicillin to treat infection of hole in tooth that I've had for a few years, and has gradually gotten worse to the point of no sleep. Should it be safe use amoxicillin to treat infection of hole in tooth that I've had for a few years, and has gradually gotten worse to the point of no sleep.