Let's pretend you wanted to give it. On the internet there are some dose recommendations of 5mg to 7.5mg per pound of body weight.
So, at 50 pounds, that is 50 x 7.5 which equals 375mg.
He ingested 560mg.
That is an overdose, but not an exceedingly high overdose.
If you had hydrogen peroxide at home and it was ingested no more than about 30 minutes ago, you could induce vomiting to get some of it out of his system.
To induce vomiting at home, give 1 to 2 teaspoons for every 10 pounds of body weight of 3% hydrogen peroxide. Do not exceed 10 teaspoons regardless of body weight. ONLY use the 3% peroxide. If no vomiting within 15 minutes, the dose can be repeated. It is an irritant to the stomach lining, and that is why it causes vomiting. 1 teaspoon is 5ml of liquid.
If no peroxide at home, I would give a full meal of food right now, even if he has ate to held protect the stomach. Giving a Pepcid A.C. antacid would also help. The dose for Pepcid antacid in a 50 pound dog is either a full tablet of a 10mg or 20mg tablet.
Wish I could do more. Hope that information helps