[souffle]

If it is a small amount I would consider giving it by mouth or in a tiny drop of baby food. You have no control over how much they drink however the vet will have factored in a dilution so you won't be able to give him the full amount they said to put in the water.
If it is Baytril it tastes horrid and some don't take the water with the taste of it. I'd ask about that when you see the vets as you don't want an infection.
Antibiotics also can destroy the gut bacteria so their digestion is not as good. A bit of live yogurt, just a drop can help.