My Cavalier King Charles Spaniel had Giardia as a pup - unfortunately all the antibiotics weakened his gastrointestinal tract and then he developed Gastritis, which is now consistently an issue.
We use holistic methods, as all conventional medicine did NOTHING to stop the diarrhea - as mentioned above, plain canned pumpkin helps...but I also use the anti-diarrhea system from Vitality Science (my holistic vet reccomended them and these have changed our life!!)
Pet Health Care - Natural Remedies For Your Cats & Dogs
it includes a very potent probiotic (PetFlora) that helps promote healthy bacteria along the gastrointestinal tract and we use the Canine Comfort daily and the herbal anti inflammatory. This helped beyond belief. I have been struggling with Louis' digestion since I got him as a pup and these methods, along with a raw diet, have worked wonders!!