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These ant traps are pretty safe in dogs and cats. The most we typically see with an ingestion is some GI upset (vomiting, diarrhea). If the package was ingested, we can also see intestinal obstructions. Most of the time they're chewed up and the bait it ingested. You can give him a dose of Pepcid AC (Famotidine) to help settle his stomach and get his appetite back. You can give 1/2 of a 10 mg tablet.
I would also try to entice him to eat to get his appetite back. You can use canned food or fishy foods. Once eating more normally, you can switch him to his normal diet. He should have a full recovery within the next 2-3 days.
I hope this helps, let me know if you have any other questions.