First I need to determine if it is large bowel or small bowel.
Has he lost any weight?
How many times a day does he defecate?
Is there any vomiting?
Is there any blood or mucous in the stool?
What kind of food are you feeding him?
What blood tests are pending?
Is he thin or under weight?
Has he lost weight or is he abnormally thin?
I am going to type for a few minutes now.
It sounds like he has small bowel diarrhea.
Here are the differential diagnosis:
PRIMARY SMALL BOWEL DISEASE
1. Inflammatory bowel disease (ex. lymphoplasmacytic enteritis, eosinophilic enteritis, and granulomatous enteritis) It is very responsive to metronidazole.
www.VeterinaryPartner.com/Content.plx?P=A&A=598 More on IBD
3. Infection (ex. histoplasmosis, salmonella, clostridium perfringens, and phythosis)
Have a sample of the feces sent off for culture and sensitvity.
4. Partial obstruction (ex. foreign body, intussusception, or a mass)
5. Small intestine bacterial overgrowth
6. Gastroduodenal ulcers
7. parasites (ex giardia, coccidia, worms)
1. Exocrine pancreatic insufficiency (ex juvenille pancreatic atrophy and chronic pancreatitis)
www.VeterinaryPartner.com/Content.plx?P=A&A=1627 more on EPI
2. Hepatobiliary disease
1. Dietary intolerance or food allergy
1. Hypoadrenocorticism www.VeterinaryPartner.com/Content.plx?P=A&A=608
3. Drug administration
If you need any of these conditions explained further, I would be happy to. It sounds like you are a MD yourself or in the medical field and I did not want to insult you.