Two forum members that I haven't seen around lately have both mentioned being on prednisone at some point. But I can't say for sure if they were drinking kava at the time or not, they were pretty regular kava drinkers though.
I found one person's answer on a google-groups page, saying that they got some relief on kava, from Prednisone induced anxiety. But they also said they preferred small xanax doses.
It doesn't appear to a combo common enough to have much info about it.