You can get it at any farm store. Used to use the pour on version on our sheep, probably got more on me than them. Never had any side effects. It can be absorbed through the skin, even the injectable version.

Of course now that news is out of it's effectiveness against the wuflu, expect some dumbass to eat an entire tube made for a horse, get sick, and then legislators to rush to make it only available from a veterinarian.