Friend, vomiting, and diarrhea can be caused by many different medical conditions. In an older dog, we need to rule out systemic diseases like kidney or liver disease, tumors, hormonal disorders, infections, etc. To determine the exact underlying cause he will need to have a hands-on examination by a veterinarian, blood work and x-rays as an initial screening test. Treatment will be based on exam and test results. I would strongly recommend having him checked as soon as you can. In the meantime, this is what you can do:
1- Do not give things like Pepto Bismol or Imodium. Start him on Pepcid AC (famotidine) 10mg 1/2 tablet every 12 hours. 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, he can continue to have water, do not feed him for 8-12 hours then offer a 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.
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