Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that your fellow received multiple doses of Meloxicam tonight.
I am very concerned for him given his age, underlying health issues (hemangiosarcoma) and the high dose he was given.
Does he normally take this medication?
A usual dose in dogs is 0.2mg/kg of body weight and then 0.1mg per kilogram every 24 hours.
He essentially received a dose of 0.75mgs per kilogram of body weight (30mgs/40kgs = 0.75mgs per kg).
Side effects from this high of a dose in a normal dog with normal organ function could range from vomiting and diarrhea to gastric ulcers, possibly perforating, and kidney failure. It can also cause increased bleeding tendencies, just what we don't want to see in a dog with hemangiosarcoma.
I am very concerned about your fellow. I recommend that he see a veterinarian for supportive fluid therapy and gastroprotectants, such as acid reducers (famotidine) and sucralfate. I would want to monitor him closely too for internal bleeding.
I understand that he seems ok now, other than diarrhea, but I am concerned that it may take several days for the full effects of this to be seen, and by then it may be too late to help him.
Please let me know if you have any further questions.