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At that dose it should just have a sedating effect. In higher doses it can be the opposite, though and there are treatments for that. But to be clear - a 100 lb. dog that ingested one 10 mg ambien will most likely just be sedated acting for up to 24 hours.
If your dog ingested this in the past two hours, you can empty his stomach by giving 3 tablespoons of hydrogen peroxide by mouth. He should vomit within 15 or so minutes. You should do this somewhere you can collect the vomit and see if you find the tablet.
Let me know if you have more questions,