As to the medullary sponge kidney, I was not aware that it was a painful condition, except
for increased episodes of
kidney stone that can be extremely painful, but only
for a few days at a time.
A University Pain Clinic will be able to manage your medication in an appropriate manner and it will never go anywhere.
As to coming off 25mcg/hr patch of Fentanyl, once you take off the patch, you will definitely have withdrawals, but not for too long.