Pepto Bismol is "bad" for ferrets because they hate it so much.  It's
used for treating stomach ailments, but it tastes so bad to ferrets and
stresses them out so much when you try to give it that the stress can
actually CAUSE stomach ailments or make the existing ones worse.  The
end result is that the stress of giving it can cause more problems than
the medicine solves.
 
Ask your vet for some Carafate (sucralfate) instead.  You usually get
it in tablet form that you have to dissolve in water, but you can find
liquid preps these days, too.  Ask your vet to find the liquid for you if
they don't have it on hand.  This is great stuff, doesn't taste bad like
Pepto, and forms kind of a temporary "bandage" on the damaged parts of
the stomach.  (Its action is nothing like Pepto's, but it is actually
better than Pepto if you're talking ulcers - damage to the stomach -
rather than just indigestion.)
 
The active ingredient in Pepto is bismuth subsalicylate.  Aspirin is
salicylic acid.  Don't let the similarity in names fool you though.
Sure, monster doses of Pepto may do some harm, but you would be very
lucky to get that much into your ferret in the first place.  The stress
of feeding it to them is what harms them.
 
Unless I've fallen behind the times (again), I believe the current
recommended protocol for stomach problems is Carafate, amoxicillin and
Biaxin.  Both antibiotics are needed to knock down the Helicobacter
overgrowth that comes with and causes ulcers - either alone will not
do the job.  The older protocol was Pepto, metronidazole and amoxi, but
the metronidazole causes the same stress problems that the Pepto does.
 
If you're seeing red blood in the stool, then you're looking at a lower
intestinal problem rather than a stomach problem.  Blood from stomach
ulcers gets partially digested, resulting in black, tarry-looking stools.
Neither Pepto nor Carafate is going to help in that case.  You will need
to point this out to your vet and have them look more urgently into why
his intestines are bleeding.  The solution may very well be surgical.
(Honestly, a proper diagnosis may have to be as well.)
 
Best of luck to you both and your kids.
 
roger (not a vet)
[Posted in FML issue 4475]