Sara,
Prednisone is a medication that decreases inflammation in the airways; it may make it easier to get out secretions but it is by increasing airway diameter and not by thinning the mucous. As for decreasing the amount of secretions I have never really heard of that? I guess theoretically it may work... but I will say that increased secretions in not an indication for Prednisone though. Prednisone does have severe side effects and is not normally used for long-term treatment for that reason. As you may be aware it causes depression, diabetes, weakens bones, and decreases immunological response. All problems we do not need making us worse! I was on it for 9 years but was taken off successfully. We tapered down the dose and switched to an every other day regimen after a couple of months. We also utilized a lot of inhaled steroids (flovent). If you doc's really want to get you off of the drug I recommend you go to an endocrinologist as well. It is completely possible to have an adrenal crisis without the Prednisone and really need to be monitored closely by a specialist.
Luke