Friend, he is not eating because he does not feel well. The big question is: Why is he vomiting and has diarrhea? This can be caused by many different 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: Pancreatitis, ingestion of a foreign body, infections, tumors or even part of a systemic disease, etc. to name a few causes. The fact that this has been ongoing since yesterday I am concern about his hydration. For this reason I would strongly recommend having him checked tonight by ER veterinarian, they can start him on supportive care (IV fluids, anti emetic, etc.) while attending veterinarian runs some testing to try to determine the exact cause for the vomiting and diarrhea. If you do not have access to ER vet this is what you can do until he is seen by family vet in the morning:
1- Do not give things like Pepto Bismol or imodium. Start him on Pepcid AC (famotidine) 10mg 1/2 tablet every 12 hours for the next 2-3 days. 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 you can offer small amount of water. Do not let him drink excessively. Then, 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, blood work and xrays as initial screening test.
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