Thanks so much for the answers to my questions.
I have several thoughts about the cause of her diarrhea based on the information provided and then I'll address your specific questions.
When presented with a dog who's had loose stools for this duration of time and blood work is negative (ruling out a systemic disease), then my list of differentials is likely to include the following:
1. Internal parasites such as whipworms, hookworms, roundworms, or giardia even though stool samples are negative for the following reason: Stool samples are not always positive when these parasites are present since eggs are not shed in every sample. So, a positive is a positive but a negative is not necessarily a negative, if that makes sense.
Studies have actually proven this to be the case even when multiple stool samples are examined. This is my professional experience as well.
2. I agree with your vet that Inflammatory Bowel Disease (IBD) is a strong possibility.
These reactions are usually triggered by the food that the dogs have eaten for a while and are usually the protein and/or the carbohydrate sources found in them.
It would take a biopsy to diagnose this problem which many owners are understandably reluctant to have done.
The signs can be intermittent but even well-controlled dogs will have flare-ups on occasion.
I usually run a gastrointestinal panel on these dogs to rule out a folate or B-12 deficiency as well as issues with the pancreas. It sounds like this was probably done already.
This condition is usually managed rather than cured but most dogs do very, very well once the right combination of food and drugs are found.
My approach to this problem would be to
1. Worm her with Panacur and Flagyl together for six days. This combination of drugs will kill all of the parasites that I mentioned.
2. Start a probiotic such as Forti-flora.
3. Change the diet. I'd feed a bland diet first, depending on the protein source in the Blue food (chicken is usually the most common ingredient in most dog foods). If that's the case, then I'd feed her boiled hamburg and rice (in a ratio of 1 to 4), small meals through the day. If I'm successful and a normal stool is obtained, then I'd recommend a food that has a totally different ingredient label. There are many, many options available in pet stores these days.
To address your specific questions:
1. I love Flagyl as a drug for diarrhea issues, especially IBD.
If I highly suspect IBD or have it confirmed and Flagyl isn't working after using it for several weeks, then I'll try Tylosin or even Pred. Three months seems excessive to me.
Most dogs tolerate this drug very well, but side effects can be seen.
To quote The Veterinary Drug Handbook by Donald Plumb:
Adverse effects reported in dogs include neurologic disorders, lethargy, weakness, neutropenias, hepatotoxicity, hematuria, anorexia, nausea, vomiting, and diarrhea. Neurologic toxicity in dogs may be manifested after acute high dosages or, more likely, with chronic moderate to high-dose therapy.
Three months could easily be interpreted as "chronic" although I have used low dose therapy intermittently for those dogs with IBD who respond to it and have an occasional flare-up.
2. We certainly can see stress diarrhea, usually colitis, especially in Shepherds but I'm not certain how much that may be playing a role here.
I've dispensed Prozac for dogs for anxiety but it can take several weeks to be effective.
3. Flagyl is the same drug humans take. I typically dispense it to my patients but it can be purchased at a pharmacy with a prescription.
I hope this helps. Deb