Friend, vomiting and diarrhea can be caused by many different medical conditions; this could be either a problem within the gastrointestinal tract or secondary to a systemic disease. The fact that he is drinking more than usual I am incline to believe this could be related to a systemic disease. You see, when a cat drinks more water than usual it is a sign an underlying medical problem. It will be difficult for me to determine the exact underlying cause without a hands on examination and some testing. But, common causes are: An active infection, hormonal disorders (diabetes, hyperthyroidism), kidney or liver disease and even cancer to name a few causes. To determine which of the above is the underlying cause your family veterinarian will need to do some blood work (chemistry profile, T4 & CBC) and urinalysis as initial screening test. Treatment will be determined by clinical and diagnostic findings. In the meantime this is what you can do for the vomiting and diarrhea:
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.
4- Follow up with your family veterinarian for a hands on examination. If cost is a concern look into your local ASPCA or Shelter where they often offer veterinary services at a lower cost.
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