In article , Cub Driver
wrote:

It turns out that the FDA does, in fact, approve drugs for the specific
purpose of veterinary euthanasia,

Isn't that sodium pentathol? (I'm not sure about the spelling.) We
once put down a St Bernard who weighed almost as much as I do, and at
the time I marveled what an easy death that was.

The standard used to be sodium pentabarbitol (Nembutal), although
thiopental would work in lower dose, it is more expensive. My
understanding is that some veterinarians use barbiturates specifically
compounded for euthanasia, rather than a standard drug.

The amount of overdose (corrected for the particular drug) and the speed
with which it's injected may have as much to do with the soeed of effect
in veterinary use. I've seen cats have their life functions stop almost
instantaneously from a large intravenous dose of pentobarbital. In
general medical practice where death is not desirable, you wouldn't give
it that fast. Pentothal and related ultrashort acting drugs like
brevital naturally act extremely fast when being dripped in at a slower
rate, which is probably safer for anesthesia.

In anesthesia, if something goes wrong, you don't want instantaneous
onset -- you want something slow enough such that if something goes
wrong, the anesthesiologist has time to react.