Its not a hazard to dogs or puppies- it is to small animals like a bunny or a bird.. It should be just fine for your puppy.
How this works is the smell associated with a bad taste. How I show a dog/puppy when you smell that smell to leave it alone is this.. First you get a q-tip- dip it in the bitter apple, let the dog smell the q tip, then with a poker face- open the dogs mouth and make a little zig zag on the dogs tongue and let the dog back out.. Remember with a puppy to later come back open the mouth then offer a treat so the puppy doesnt associate you with opening the mouth as unpleasant.. ( unless that smell is attached..)