Friend, when we see blood in the stool this is a sign of inflammation in the colon (large intestines). The vomiting and diarrhea are a consequence of the inflammation. This can be caused by many different medical conditions. It will be difficult for me to determine the exact underlying cause without a hands on examination and some testing. But, common causes are: Dietary indiscretion, ingestion of a foreign body, infections or even part of a systemic disease (kidney, liver, etc.) to name a few causes. To determine the exact underlying cause he will need to be seen by family veterinarian for a hands on examination, blood work, urinalysis and +/-xrays as initial screening test. Treatment will be based on exam and test results. In the meantime, in any case of vomiting or diarrhea the first thing to do is give the gastrointestinal tract time to rest. This is what you can do:
1- Do not give things like Pepto Bismol or imodium. Start him on Pepcid AC (famotidine) 10mg 1/4 tablet every 12 hours. You can buy Pepcid AC over the counter in any pharmacy.
2- No food or water for 4-6 hours. Need to give his gastrointestinal tract time to rest.
3- After 4-6 hours offer a small amount of water. Wait half hour, if no vomiting, offer small amount of rice (50%) and boiled boneless chicken or ground beef (50%) 4-6 times a day.
4- Follow up with your family veterinarian for a hands on examination in the morning.
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