I have allergic reaction to erythromycin, would i expect a reaction to taking azithromycin?

Low likelihood: While both of these antibiotics are macrolides, erythromycin has a 14 carbon lactone ring and azithromycin has a 15 carbon lactone ring. The likelihood is low for cross reactivity, however, a board certified allergist can provide strategies to assess this. Skin tests may be helpful, yet are not standardized so a graded challenge may be necessary.