I am allergic to penicillin. Several years ago, I took erythromycin for chin acne. After a few days, I broke out with an itchy rash on my neck and stopped the meds. I've taken azithromycin since then with no trouble. Today I was prescribed clarithromycin for strep. Since I had azithromycin a few weeks ago for something else I couldn't get it again. I just found out azithromycin, erythromycin and clarithromycin are all from the same family. What are the odds I will have a reaction to clarithromycin?