A dog can basically take the same meds as a human. They can also take the same dose for a person or child of the same weight. Some Vet School Pharmacies will give you dosing info over the phone.

Cats are another matter while they can generally take the same meds the dose is quite different. They don't metabolize meds as quickly as dogs or humans and they can overdose really quickly. A vet will generally tell you a cat can't take Aspirin but they can. Their does is about 1/4 of a REGULAR Aspirin every THREE days. I just don't ever give my cat Aspirin. Even if the Vet orders it I tell him if she is in enough pain to need a med then let's give her something made for cats (dosage wise) and I don't have to worry about giving too much to her too soon.

As far as kids go....a lot of the older Pediatricians are better about giving kids meds when they need it. I have a friend that takes her kids to the doc she saw growing up. One of them had a horrible ear infection and he got Paragoric for the ear pain when Liquid Tylenol #3 didn't work.