Apparently, your physician decided that the necessity of taking a dye scan was worth the risks of a
reaction, and tried to make sure the
reaction was dampened. The
prednisone will work itself out fairly raopidly, although usually, one "tapers down". Prednisone depresses the immune response, which could make one more susceptible to a viral or bacterial infection in the lung. There should no long-term harm from a single use of prednisone, even at such a high dose.