That's a big dog.
In the future, if you still have poison control, that's the sort of question you can call and ask. I once called because my 90 pound dog had gotten a hold of my then boyfriend's really strong anti-ulcer medication. At first they were in a bit of a panic because I accurately described Bob the dog as a 6 month old puppy....when I got to the part about him weighing 90 pounds they stopped worrying and told me to do what you did: monitor him for the night and, yes, give lots of liquids.