It's the most commonly used anti-biotic they give you at the vets. I had it for Nagini's R.I once.
I think it's similar to the paracetamol the school nurse gave you. It didn't matter what you went in for- headache, stomach ache, broken leg, bunsen burn on your arm, compass in your eye etc- you always got a paracetamol and told to get back to class.