Sorry to be so abrupt but ibuprofen, the active ingredient
in motrin, is EXTREMELY toxic to
dogs! Even a small dose can lead to events that will kill him.
It's best to check with your vet first on dosing, but he CAN have human aspirin as long as it's either buffered or enteric coated, like Ascriptin. But don't give him any other type of human OTC pain reliever because they are just not formulated for dogs.