There could be a few different causes, and the IBD that you mention
that the first vet diagnosed could be a cause. That would explain why
prednisolone helps, as if relieves the inflammation. However, treating
every day with pepto bismol is just putting a band aid on a big wound,
and pepto is not a good thing to be giving anyway, as it has an
aspirin-like ingredient that isn't good for ferrets.

Two suggestions:

First, replace the pepto bismol with Pepcid AC, which has only one
active ingredient, Famotidine, which is safe for ferrets. Dissolve one
10-mg Pepcid AC tablet in 4.0 ml of water and give the ferret 0.25 -
0.4 ml 2 or 3 times a day, as needed, with the dosage depending on his
weight and the severity of his problem. Store the liquid in the fridge
and stir before using, as the dissolved tablet can settle at the
bottom.

Second, give him some probiotics. He's probably not producing enough
'good' bacteria anyway, which is needed for proper digestion, and the
use of antibiotics is killing off what little 'good' bacteria he may
have. The smell in the poops probably is excess bacteria, and the
diarrhea is improperly digested food. Probiotics improve digestion and
can help both problems. I have had great success using Forti-Flora for
felines. I've also used plain acidophilus, and I know others who have
used Bene-Bac. If you feed him some kind of soup, then any of these can
be dissolved in water and included with the soup. If interested, write
to me and I'll forward the link online where I buy the Forti-Flora.
Acidophilus is in any drugstore or grocery store and is very cheap.
Use about 1/4 tablet daily, then once every other day when symptoms
improve.

As a final possibility, carafate (sucralfate) can also help to soothe
the stomach and to bind poops.

Jeff
In Memory of Neo, Trinity, Possum, Misty, Frodo, Baggins, and Mr.
Parker Caring for Luna, Morphy, Baby Girl, Dozer, Pop, Sabrina, and
Minnie Mouse

[Posted in FML 6754]