The purpose made neuromuscular blocking drugs (curare derivatives, aminosteroids, succinylcholine) can only be given by injection.
How about injectors built into a cloud of nanobots? Those 'bots which make it inside any particular victim network with each other (possibly using the victim's own nervous system?), evaluate the dose needed to effect him/her and then deliver that *exact* dose.
--
Richard Aiken
"Never insult anyone by accident." Robert A. Heinlein
"I studied the Koran a great deal. I came away from that study with the conviction there have been few religions in the world as deadly to men as Muhammed." Alexis de Tocqueville
"We know a little about a lot of things; just enough to make us dangerous." Dean Winchester (fictional monster hunter portrayed by Jensen Ackles)
"It has been my experience that a gun doesn't care who pulls its trigger." Newton Knight (as portrayed by Matthew McConaughey), to a scoffing Confederate tax collector facing the weapons held by Knight's young children and wife.