Friend, naproxen toxicity in dogs is very dependent on the amount consumed and weight of the dog. Doses of 5mg/kg and above will cause gastrointestinal ulceration. Doses above 10 mg/kg can cause kidney failure. In this case, your dog based on her weight took a dose of 42mg/kg; at this dose she is likely to develop gastrointestinal ulceration which explains the vomiting. In addition, she may go into kidney failure which also causes vomiting.
Unfortunately in this case we are very limited as to what you can do at home. I would highly recommend having her checked tonight by ER veterinarian to start her on supportive care of IV fluids, anti emetics, etc. or this could be fatal for your dog. If you do not have access to ER vet this is what you can do until she is seen by family vet in the morning:
1- Do not give things like Pepto Bismol or imodium. Start her on Pepcid AC (famotidine) 10mg 1/4 tablet every 12 hours. You can buy Pepcid AC over the counter in any pharmacy.
2- If she is able to keep water down keep her off food for the next 8-12 hours. Need to give her gastrointestinal tract time to rest.
3- After 8-12 hours 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 supportive care. 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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