Obviously I’m not a vet and this is just my experience but I really think the Zithromax should be given a go. You’ve tried Baytril so you’ve got nothing to lose. My Pepper had a two week course of Baytril and it didn’t do anything and the abscess got so much larger. Pepper had a long course of Zithromax. 6 weeks but it did suppress his appetite while he was on it and he needed syringe feeding.