Friend, vomiting 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: A simple gastritis, dietary indiscretion, ingestion of a foreign body, infections or even part of a systemic disease, etc. to name a few causes. The fact that he has been vomiting since Friday and not able to keep water down I am really concern about his hydration. I would strongly recommend having him checked today by ER veterinarian to start him on supportive care (IV fluids, anti emetics, etc.) while attending veterinarian runs some testing to determine the exact underlying cause of the vomiting. If you are not able to get in to see a vet today 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 1/4 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 3-4 hours. Need to give his gastrointestinal tract time to rest.
3- After 3-4 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. Keep on this diet for several days then wean into regular diet.
4- Follow up with your family veterinarian for a hands on examination, blood work and xrays as initial screening test.
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