Prednisone is converted into prednisolone in the body (I think it's that way round, anyway, might have it back to front). From speaking to people on here, the side effects of prednisolone tend to be less severe than prednisone. Also it seems that prednisolone is used at a slightly lower dose, but that could just be the doctors (since prednisolone is used more in the UK, and prednisone in the US).