I think Ketamine just wears off and it’s pretty short-acting. Vets use Immobilon which can be injected by dart gun. That has to be reversed with an equal dose of Revivon. The strength of Immobilon used for large animals is lethal if accidentally injected into humans. I recently met a veterinary nurse who once had to keep her boss alive after he accidentally scratched his hand with the needle on a syringe-full of the stuff. she had to inject him with Revivon and then give him CPR until the paramedics arrived. He survived, but it was touch and go.
All of which means, I suppose, that it’s too drastic for what you want, Tim. This link might help, although double-check the data:
http://en.wikipedia.org/wiki/Dissociative_drug
And failing that, try contacting SciTalk:
http://www.scitalk.org.uk/
Good luck
Dee