Prednisone is broken down to prednisolone in the liver. The prednisolone is what has the effect on the tumors. As long as the ferret has a healthy liver, either one will work just fine, and prednisone is less expensive. If the liver is marginal, the extra load of converting the prednisone can be problematic, and I've heard of cases where in ferrets with poor liver function, the conversion didn't happen, or wasn't efficient, so the prednisone didn't have the desired impact. Kevin Farlee [Posted in FML 7472]