with the Pemphigus, but have you tried other immuno-suppressants in the past?

One of the preferred treatments is with Azathioprine, although that one can be hard on the liver. Cytoxin and Leukeran are also drugs that are used routinely.

A possible thing try that you should discuss with your Vet is to start tappering the Prednisone while starting on Leukeran at a low dose. As you continue to decrease the Prednisone, increase the Leukeran. Over a period of weeks if not months you might be able to reduce the Prednisone down to a very low level, while depending on Leukeran to keep the Pemphigus under control. The main side affect of the Leukeran will be myelosuppression or bone marrow suppression. Don't believe it will cause the liver any problems, but of course you would have to monitor for it. Else it's the rock and the hard place.