Do NOT add in Brewers Yeast with insulinoma.  Raising the chromium levels
above the amount in foods (which is what it does) LOWERS blood sugar
levels, so it is useful for diabetes but exactly the opposite of what
you want with insulinoma.  Years ago people thought it was just good for
the pancreas, but that was because of use for diabetics.  Once more was
known it was realized that it is not good for insulinoma but can be for
diabetes.
 
The meds used for insulinoma if the ferret is not a surgical candidate or
if the vet prefers meds are Prednisolone and Diazoxide.  Some vets begin
with both, and some begin with just Prednisolone and then later add
Diazoxide.  Expect the medication levels needed to change over time and
to have a number of repeat appointments over time.
 
I recommend this for you:
http://www.afip.org/ferrets/index.html
[Posted in FML issue 4671]