Email Article. Azithromycin is a broad-spectrum antibiotic of the macrolide class, used to treat susceptible bacterial infections in dogs, cats and other pets. Use all of the medication prescribed, or the infection is likely to recur or become worse. Contact your veterinarian if your pet experiences vomiting, diarrhea, or jaundice (yellowing of the gums, skin, or whites of the eyes) while being treated with azithromycin.