That could be lethal. He needs to be seen right away.
You should have made him vomit! I am not sure what that medication is and now it has been 5 hrs so I assume it has passed although hopefully you called a vet. For future to make a dog vomit you can give him some hydrogen peroxide that you get at the store then run him around and it will bubble up and make him vomit - Although do not do this for things that could be more harmful coming back up! Hope everything is ok!