The problem is that in most cases pouchitis is NOT an infection. So taking antibiotics other than orally is not really a good option (unless you have signs of systemic disease like chills and fever). In most cases it is an inflammatory response to the presence of normal bacteria. If you take broad spectrum antibiotics, especially by injection or IV, you alter your normal body bacteria all over your body. This is OK when you have a specific infection, like bronchitis, but if you don't, you are risking other infections by killing off your normal flora that is very important for keeping pathogens in check.
You probably need other Crohn's treatments, and maybe even perpaps pouch removal if these are not successful. Crohn's of the pouch is one of the more common causes of pouch failure. Have you tried 6-MP, methotrexate or any of the biologics?
I would suggest you seek a GI with more experience with IBD treatment.
Jan