Regarding propofol, it needs to be IV and yes, it stings quite a bit even when mixed with a little lidocaine. The volume needed for anesthetic induction is fairly high, too -- a typical 70 kg person takes 7-8 mL of the stuff to go under. It does work within seconds and wears off in a couple minutes. However, rapid IV doses, such as we use to induce anesthesia, do tend to make the person stop breathing. That's not a problem in the operating room -- it would probably be bad for your plot, though. (In case you're wondering what we do when the propofol wears off, we generally start anesthetic gas before the patient awakens and then continue to keep the patient asleep with gas: it's much more unpleasant to be anesthetized with gas then with an IV drug.)
Anything you would inject into a muscle (such as a narcotic or ketamine) takes a couple of minutes at least to work, even with a monster dose. Overall, I can't think of anything that would suit your needs of a non-IV drug with immediate action and rapid reversability. As George suggests, you might just make something up or not specify what it is.
