Any vomiting yet? If not, you can repeat that peroxide dose once. I don't think you will see many issues from this ingestion. During part of the clinical studies for this drug, it was given at 90mg per pound (that would be 900mg for him) for 1/2 to a full year. Cataracts
where the only abnormality noted (that I can find in the study - it was very long). After inducing vomiting, I would watch him for any constipation, severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); chest pain; dark urine; muscle
pain, tenderness, or weakness (with or without fever or fatigue); pale stools; red, swollen, blistered, or peeling skin; severe stomach pain; yellowing of the skin or eyes
. This information is from drugs.com and is extrapolated from human side effects. If any of this is see, have your vet evaluate him immediately. Please let me know if you have any other questions. Hope this helps.