My vet prescribes Baytril but no steroids, she believes a steroid could actually cause more harm which she does have a point but many other vets do prescribe a steroid along with a antibiotic.
Prednisone is good with inflammation but it also weakens the immune system which can then be detrimental to the rat when fighting a big infection. You could also try metacam.
I usually use baytril and doxy for my abs and a steroid for a few days to reduce inflammation.
Doxycycline also has anti-inflammatory properties as well.