Kathy, Mr Tinkles is on Zithromax for a chronic URI, not stomatitis. I don't know anything about stomatitis, just about the antibiotic itself. My vet suggested Zithromax to me, after two courses of Amoxicillin didn't clear it up. He is on a 6 week course, so refilling every 10 days was going to be very expensive. A member of this board was using it for a URI also, and gave me ideas about compounding pharmacies to look into. If you need a longer course than 10 days, it's worth looking into getting it compounded.
You might get more suggestions and help if you put Stomatitis in the title of the thread. I'm sure there are members here who have experience with it, and may have other ideas for you.